Patent ID: 7367762

Claim:
A main spindle apparatus, comprising: a main spindle having a through hole in an axial direction thereof; a main spindle head rotatably supporting the main spindle therein; a tool holder clamp unit including: a unit main body having a tool mounting hole to which a tool holder is mounted; a clamp mechanism for clamping the tool holder; and a bias mechanism for biasing the clamp mechanism in a clamping state; and a clamp release mechanism provided on the main spindle head side, the clamp release mechanism releasing the clamping state of the clamp mechanism by operating the bias mechanism, wherein the tool holder clamp unit is mounted in the through hole of the main spindle so that the tool holder clamp unit is removable from a front side of the through hole of the main spindle, wherein a single step is provided inside the main spindle so as to define a small diameter portion positioned on a rear side of the main spindle and a large diameter portion positioned the front side of the main spindle, wherein the bias mechanism is positioned at the small diameter portion when the tool holder clamp unit is mounted in the through hole of the main spindle, and wherein the large diameter portion houses the unit main body and the clamp mechanism.