A spindle device comprising: a housing; a spindle of which a part close to an axial end is rotatably supported to the housing by a rolling bearing or a rolling bearing unit and of which an axial end portion is mounted with a tool when in use; and an electric motor configured to rotatively drive the spindle; wherein the electric motor is configured such that an inner peripheral surface of a stator supported to the housing faces an outer peripheral surface of a rotor supported and fixed to an axially intermediate portion of the spindle; wherein a radially central portion of the spindle is formed with a through-hole configured to axially penetrate the spindle, and wherein an axial end portion of the housing close to said axial end is provided with a closing plate, characterized in that radial venting holes enabling an outer peripheral surface and an inner peripheral surface of the spindle to communicate with each other are provided at a plurality of circumferential locations of a part of the axially intermediate portion of the spindle closer to said axial end than a part of the axially intermediate portion of the spindle, to which the rotor is supported and fixed, that axial venting holes enabling the axial end face of the spindle and inner peripheral surfaces of the respective radial venting holes to communicate with each other are respectively provided at a plurality of circumferential locations of said axial end portion and extend towards the axially intermediate portion of the spindle, that discharge holes enabling the outer peripheral surface of the spindle and inner peripheral surfaces of the respective axial venting holes to communicate with each other are respectively provided at a plurality of circumferential locations of a part close to one axial end of the spindle and positioned closer to said axial end than a part close to said axial end of the spindle, to which the rolling bearing or the rolling bearing unit is externally fitted, that an outer diameter-side opening of each radial venting hole is closed by an inner peripheral surface of the rolling bearing or the rolling bearing unit or another member externally fitted and fixed to the outer peripheral surface the spindle, that an inner peripheral surface of the closing plate closely faces the outer peripheral surface of the part close to said axial end of the spindle, at a location between the part to which the rolling bearing or the rolling bearing unit is externally fitted and the part at which the respective discharge holes are provided, via an annular gap, that an outer diameter-side opening of each discharge hole is positioned at a more radially inner side than one axial side opening of the annular gap, and that when using the spindle device, a cooling gas can be fed from the opening of the through-hole at the other axial end of the spindle and is discharged from each discharge hole through each axial venting hole and each radial venting hole. a housing; a spindle of which a part close to an axial end is rotatably supported to the housing by a rolling bearing or a rolling bearing unit and of which an axial end portion is mounted with a tool when in use; and an electric motor configured to rotatively drive the spindle; wherein the electric motor is configured such that an inner peripheral surface of a stator supported to the housing faces an outer peripheral surface of a rotor supported and fixed to an axially intermediate portion of the spindle; wherein a radially central portion of the spindle is formed with a through-hole configured to axially penetrate the spindle, and wherein an axial end portion of the housing close to said axial end is provided with a closing plate, that axial venting holes enabling the axial end face of the spindle and inner peripheral surfaces of the respective radial venting holes to communicate with each other are respectively provided at a plurality of circumferential locations of said axial end portion and extend towards the axially intermediate portion of the spindle, that discharge holes enabling the outer peripheral surface of the spindle and inner peripheral surfaces of the respective axial venting holes to communicate with each other are respectively provided at a plurality of circumferential locations of a part close to one axial end of the spindle and positioned closer to said axial end than a part close to said axial end of the spindle, to which the rolling bearing or the rolling bearing unit is externally fitted, that an outer diameter-side opening of each radial venting hole is closed by an inner peripheral surface of the rolling bearing or the rolling bearing unit or another member externally fitted and fixed to the outer peripheral surface the spindle, that an inner peripheral surface of the closing plate closely faces the outer peripheral surface of the part close to said axial end of the spindle, at a location between the part to which the rolling bearing or the rolling bearing unit is externally fitted and the part at which the respective discharge holes are provided, via an annular gap, that an outer diameter-side opening of each discharge hole is positioned at a more radially inner side than one axial side opening of the annular gap, and that when using the spindle device, a cooling gas can be fed from the opening of the through-hole at the other axial end of the spindle and is discharged from each discharge hole through each axial venting hole and each radial venting hole.