Spindle apparatus for machine tool

A spindle apparatus of a machine tool, comprising:

• a motor configured to rotatably drive a spindle;
• a motor accommodation section having a cylindrical inner wall surface configured to accommodate the motor;
• a headstock including a spindle housing fixed to an outer wall surface of the motor accommodation section so as to surround the outer wall surface to form a cooling passage for passing a cooling medium between an inner wall surface of the spindle housing and the outer wall surface of the motor accommodation section and an attaching section configured to be attached to a moving member or a fixed member;
• and
• a cooling medium accumulation part being integrally formed with the spindle housing and the attaching section between the spindle housing and the attaching section, the cooling medium accumulation part having a box shape and including a top wall, a bottom wall and side walls configured on the attaching section, the top wall having a first inner surface, the bottom wall having a second inner surface, and the side walls having third to sixth inner surfaces, the box shape being formed by the first to sixth inner surfaces, most part of the cooling medium accumulation part being beneath the headstock, wherein
• at least a width of the cooling medium accumulation part in a direction perpendicular to the spindle is wider than a width of the motor accommodation section in a virtual projection plane obtained by projecting the cooling medium accumulation part in a direction from the spindle housing to the attaching section,
• a straight through-hole communicating the cooling medium accumulation part and the cooling passage directly is formed in a side wall part of the spindle housing, and
• the cooling passage is bisected at a middle of the straight through-hole.