A workpiece machining apparatus including a headstock to which a workpiece having a through-hole extending in a Z-axis direction is attached; a tool rest which is movable in the Z-axis direction and in an X-axis direction; and a rotary tool unit which is attached to the tool rest, is provided. The headstock has a support member which is movable in the Z-axis direction and which has a spindle side contact portion in an end portion in the Z-axis direction. The rotary tool unit has a tool body having a tool side contact portion with which the spindle side contact portion can come into contact in the Z-axis direction, and a rotatable tool which protrudes from the tool body. The rotating tool machines the workpiece by moving the tool body in the Z-axis direction in a state where the spindle side contact portion and the tool side contact portion are brought into contact with each other.