In order to contribute to the study of the generation process of the Hyuga Nada earthquakes and the magma supply process to volcanoes such as Sakurajima and Kirishima, we conducted linear array observations, receiver function analyses and seismic tomography, and estimated the seismic structure of the Philippine Sea slab beneath southern Kyushu. The continental Moho is clear in the middle to western part of the southern Kyushu, however it becomes unclear near the mantle wedge in the eastern part. This suggests that the seismic velocity is low in the mantle wedge due to the fluids discharged from the oceanic crust. The oceanic Moho in the Philippine Sea slab is clear up to the depths of 100 – 120 km and it bends convex upward at ~60 km. There exist low velocity anomalies in the vicinity of Kirishima, Sakurajima and Kaimondake volcanoes at 10 km depth. The oceanic crust shows low velocity at 30 - 40 km depths, however it turns high velocity at 50 – 60 km depths. This can be explained by eclogitization of the oceanic crust.