To provide a motor built-in type spindle device that can suppress an increase in temperature of a rotary shaft and a bearing, which is caused by the heat released by a rotor, and can improve processing accuracy.

In the motor built-in type spindle device 10, the rotary shaft 12 includes: a first cylinder 71 disposed with the rotor 20 on the outer periphery thereof and formed of a carbon fiber composite material; and a second cylinder 72 disposed with the first cylinder 71 on the outer periphery thereof and formed of a metallic material.