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The Kashiwagi Unit is the youngest unit in the Northern Chichibu accretionary complex. In this study, we measured zircon U-Pb ages from sandstone and felsic tuffaceous phyllite in the Kashiwagi Unit to determine their depositional ages. As a result, we obtained depositional age of 128.2±1.4 Ma and 126.7±2.0 Ma from two sandstone samples and 134.2±1.5 Ma from a felsic tuffaceous phyllite sample. The depositional age of this unit was previously estimated by radiolarian fossils from shale and siliceous shale, presenting a wide range from the Middle Jurassic to Early Cretaceous. The zircon U-Pb ages from the sandstones are assigned as the Early Cretaceous, presenting younger than the radiolarian age. Detrital zircon U-Pb ages of sandstone suggest that the uppermost age of the ocean plate stratigraphy of the Kashiwagi Unit is younger than the Barremian age.