A seismic experiment with 6 explosive sources and 391 seismic stations was conducted in August 2001 in the central Japan region. A large lateral variation of the thickness of sedimentary layer was observed. P-wave velocity values below the sedimentary layer obtained were 5.3 km/s ~ 5.8 km/s. P-wave velocity values at the lower part of upper crust and lower crust are estimated to be 6.0 km/s ~ 6.4 km/s and 6.6 km/s ~ 6.8 km/s, respectively. Two clear later phases were observed at the record section of shot-J5. The phases are interpreted to be reflected waves at the boundaries with depths of about 10--20 km and 20--35 km. The dip angle of the deep boundary is about 26¿. The shallower reflector is interpreted to be a lithological boundary. The deeper reflector is the upper boundary of subducting Philippine Sea plate. The configuration of the subducting Philippine Sea slab was revealed.