In order to clarify climatic regionality in relation to synoptic meteorological phenomena, the daily duration of sunshine and the daily mean temperatures at about 140 sites in Hokkaido are analysed with time variation (day-to-day variation). Both principal compo-nent analysis and cluster analysis using factor loadings are applied. The values of the factor loadings correspond to the correlation coefficients between the principal component and the climatic element of each point, and also indicate the time coefficients between them. The daily data for 1978_??_1980 were used in this study. Each datum was converted into a deviation from the areal mean for each day. The data for 1978 were mainly used for the analysis, although the results were compared with those for other years to examine the propriety of the results. The first three dominant patterns of the daily variability of sunshine duration account for more than 50% of the total variance. The first eigenvector (24.8% of the total vari-ance) depicts the area of positive (negative) departure to the northwestern side of Ho-kkaido with the area of negative (positive) departure to the southeastern side (Fig. 2-a). The positive pattern (i, e., the total duration of sunshine over the area with a positive sign is relatively greater than that of the area with a negative sign) prevails in summer. This is due to the reduction of sunshine in the southeastern side as is influenced by cyclon-es passing through the southeast of Hokkaido or by sea fogs which are caused when southeasterly warm monsoons blows over the cool Chishima Current. In winter the nega-tive pattern prevails; it reflects the diminution of sunshine in the northwestern region as is influenced by snow clouds accompanying winter monsoons. The second eigenvector (17.2% of the total variance) indicates the contrast between the northeastern side (Okhotsk side) and the southwestern side (Donan side) of Hokkaido (Fig. 2-c). Each of these positive or negative patterns is formed with the influence of both the front and the passage of cyclones in the warm season. The pattern of the third eigenvector (9.3 % of the total variance) describes three areas, i. e., one positive area which extends from the northeast to southwest with two negative areas on either side (Fig. 2-e). This positive pattern appears clearly in summer. It is formed with the influence of both the sea fog mentioned above and cyclones passing over the north of Hokkaido. Furthermore, this pattern tends to appear at the same time as the first component of the sunshine duration has a dominant positive value. On the other hand, the negative pattern, which is caused with the influence of fronts passing over the center of Hokkaido, does not turn out clearly. From these results, four regions with different time variation types of sunshine duration are pointed out. These are the Pacific side type, the Japan Sea side type, the Sea of Okhotsk side type, and the Donan side type (Fig. 8). Especially, the southeastern side of Hokkaido which is belonging to the Pacific side type has fairly specific regional properties of the sunshine duration in comparison to other regions. The first three eigenvectors of daily mean temperature variations account for 43.1%, 14.4%, and 10.6% of the total variance, respectively (i. e., cumulative for 68.1% of the total variance). The pattern of the first eigenvector which distinguishes the inland area from the coastal area is caused by the land-sea heating contrast (Fig. 4-a). The distribution pattern of the second eigenvector closely resembles that of the first eigenvector of the sunshine duration (Fig. 4-c). Both positive and negative patterns prevail in early summer and winter, whose causes are explained by the cooled or warmed wind over the sea in each season.