To keep rotational accuracy by absorbing thermal displacement of a spindle in a spindle device of a discharge machine for performing high speed rotation and rotating angle indexing in a simple constitution without applying load to a bearing.

This spindle device of a discharge machine is so constructed that a spindle is rotatably supported by a front bearing and a rear bearing through an inner ring spacer in a bearing case of a machining head, designated pre-pressure is applied to the front bearing to support the thrust force of the spindle, and the spindle is driven in rotation by a motor provided in the rear direction. In the device, the rear bearing case is integrally fixed to the inner peripheral part of an annular thin disc member right-angled to the axial direction, and the outer peripheral part of the annular thin disc member is connected and fixed to the bearing case.