The flow of goods between retail stores and final consumers may be considered from two standpoints: from the standpoint of the store and from that of the consumer. The sales activity of the store may be analyzed according to the two aggregative concepts of a central place and its market area. It has been assumed in this paper that city households as final consumers actively select stores, while the retail store passively await selection by the consumer. This study focusing on the buying behavior of the active consumer utilizes two concepts of a store cluster and a basic unit area. The store cluster represents the group of shopping facilities used by the consumer. The basic unit area represents the household group of consumers located similarly in relation to commercial environment (i.e. store clusters) and therefore using similar store clusters. Thus, the purchasing activity of city households may be expressed as the relation between basic unit areas and store clusters. Using such a form, this paper attempts to identify patterns in shopping behavior and explore the internal structure of city-level trade area generally. Kazo City, Saitama Prefecture, was the study area for this survey conducted through elementary schools within its legal limit. The survey disclosed that Kazo City households use three types of store clusters: neighborhood store cluster, a store cluster located along the approach to the Kazo central shopping street, and a core store cluster in Kazo central shopping street. On the basis of frequency of purchase, consumer goods may be divided into three types: daily needs, items purchased monthly, durable goods which usually need not be purchased more often than annually. Goods purchased daily would consist of food stuffs. Goods purchased monthly would be drugs, clothes and electric appliances. Goods purchased annually would be such items as furnitures and clocks. As for distribution of purchasing frequency, goods purchased daily represent 88%, goods purchased monthly 11%, and goods purchased annually 1%. Obviously daily needs are met most frequently. Shopping patterns seem to be correlated with the distance between basic unit area and the central shopping street. Designate as A the number of foodstuff stores in a neighborhood store cluster used during a three day period by an average household in a basic unit area. Designate as B the number of foodstuff stores in store clusters (not including those in neighborhood store clusters) used during a three day period by an average household in a basic unit area. In a basic unit area located within a 4_??_6 kilometers radius from Kazo's central shopping street, the households buy almost all daily shopping goods in their respective neighborhood store clusters (3 B_??_A). Goods purchased monthly are bought in the store cluster along the approach to the central shopping cluster, and goods purchased annually are bought in the central shopping cluster. On the other hand, the tendency for purchase of foodstuffs drops for the basic unit area located in a 3_??_4 kilometer radius from the Kazo central shopping street (B<A<3 B). That is, consumers living within this radius tend to use medium-size foodstuff stores in the store cluster along the approach, and large self-service store in the core store cluster. Those living in the basic unit area within a 2_??_3 kilometer radius purchase foodstuffs in neighborhood store clusters even less frequently (A_??_B). These purchasers tend to buy foodstuffs in stores located along the approach, or frequently at the big self-service food stores in the core store cluster. Thus, the internal structure of the Kazo City trade area consists of concentric areas each composed of basic unit areas. In this study of city level trade area and its internal structure, patterns of consumer shopping behavior have been emphasized.