The present invention provides a cartridge-type spindle device having an easily separable structure despite the fact that it comprises a rotary joint for a through spindle coolant device. In the cartridge replacement type spindle device (11), front bearings of the spindle are built in a front housing (23) and rear bearings of the spindle (15) are supported on a rear housing (25) so that, when the front housing (23) is separated from the rear housing (25), the front bearings (17a, 17b), the spindle (15), and the rear bearings (19a, 19b) can be separated from the rear housing (25) integrally with the front housing (23). The rotary joint is disposed in a piston (63) of an unclamp means for unclamping a tool (21, T) mounted to the forward end of the spindle (15), so that a draw bar (51) accompanied by a seal ring can be separated from the rear housing (25) and the rotary joint together with the spindle (15) and the front housing (23).