To provide a conventional hydraulic expansion chuck at low cost, having a hydraulic expansion chuck mechanism incorporated into a chuck body, provided with a cylindrical inner wall across the board, and having an expansion clamp bushing with no radial through-holes.

A hydraulic expansion chuck includes a hydraulic expansion chuck mechanism 23 incorporated into a chuck body 20. The hydraulic expansion chuck mechanism 23 has an expansion clamp bushing 23a provided with a cylindrical inner wall across the board, and a reducing bushing 24 disposed in the expansion clamp bushing 23a for housing a shank tool, particularly a screw tap. The reducing bushing 24 is unrotatably connected to the chuck body 20 by geometric connection on the outer circumferential side and unrotatably connected to the shank tool by geometric connection on the inner circumferential side.