To simplify the structure and reduce the size of automatic tool changers than by conventional methods, and shorten their time to process workpieces with a series of tools.

The automatic tool changer makes changes of tools T between a tool magazine 12 and a spindle 4 rotatably supported on a spindle head 5 movable in the Z-axis direction along the spindle axis and the X-axis and Y-axis directions both perpendicular to the Z-axis direction. A tool change arm 15 is rotatable on an axis parallel to the Z-axis and has two tool grippers 15A and 15B extending radially from the axis of rotation in a preset angular relation. A servomotor 16 rotates the tool change arm 15 on the axis of rotation through an arbitrary angle.