Two sedimentary cycles can be recognized from the late Pleistocene “Miwa Formation” of the Shimosa Group in the Ishioka-Hokota area, Ibaraki Prefecture, by analyzing depositional facies, tephra key beds and erosional surfaces. The lower cycle consists of an incised-valley fill depositional system, which is limited in the western part in distribution and the overlying shoreface-beach system distributed throughout the studied area. The upper cycle is characterized by a widely-distributed back-barrier system, which has thickly been preserved in the western part, whereas had been much eroded by an overlying shoreface-beach system in the eastern part. The following Joso Formation is composed mainly of fluvial deposits, though marine beds are found in the lower part of the eastern area. The two sedimentary cycles in the “Miwa Formation” correspond to two depositional sequences determined by the upper and lower sequence boundaries (SB1, SB2 and SB3). The two depositional sequences include transgressive and highstand systems tracts, and contain two erosional surfaces: bay ravinement surface and wave ravinement surface.