The characteristics of the earth pressure acting on a retaining wall are investigated on the basis of the large scale prototype tests in a field. The wall is made of concrete and 10 M in height. The silty sand and the slags are used as the backfill materials. The measured earth pressure at rest and change to the earth pressure in the active and passive states are shown. The influence of displacement of the wall on the magnitude and the distribution of earth pressure in the vertical direction are shown and discussed. The co-efficient of earth pressure, the angle of wall friction and the point of application of resultant earth pressure are also examined. Based on the new informations obtained from the tests, the design philosophy of a retaining wall is considered and it is proposed that a general retaining wall should be designed against the earth pressure at rest. Finally the measured earth pressures are compared with the analyzed results by fem. /Author/TRRL/