Abstract: A spindle apparatus capable of exhibiting a good interchangeability of a tool holder without any necessity for managing a gap between an end surface of the tool holder and an end surface of a spindle shaft and, besides, obtaining a high tool holding rigidity. Small- and large-diameter portions are formed in the outer surface of the spindle shaft having a taper hole formed in the shaft end. A sleeve formed with a fluid passageway communicating with the outside is fitted, with interferences, to the outer surface thereof. On the other hand, a flange having a diameter larger than a taper shank is provided at a proximal portion of the taper shank of the tool holder. A fluid pressure is applied to the fluid passageway of the sleeve, thereby making the sleeve contact with the flange of the tool holder that is fitted to the spindle shaft. Thereafter, the sleeve is fixed to the spindle shaft by removing the fluid pressure, and the tool holder is supported with a high rigidity.