To suppress intrusion of lubricating oil from a through-hole of a seal plate toward a compressor impeller.

A supercharger includes a supercharger body, a turbine shaft 7, a bearing 20 comprising either a radial bearing 21 or a thrust bearing 22 or both of them, a seal plate 27, and an oil thrower 28. The seal plate has an annular projection 27 centering the turbine shaft, which projects from a back face 27b located oppositely to the side of the plate facing the back face 9a of a compressor impeller 9, in the axial direction of the turbine shaft. In the outer circumferential face 27e of the projection, at least a part vertically above the turbine shaft is provided with a guide part 27f which extends along the circumferential direction of the projection and projects or recesses in the radial direction of the turbine shaft to guide lubricating oil depositing on the back face of the seal plate to bypass the through-hole 27a and to flow vertically downward.