Abstract: A positioning apparatus can perform high-accuracy positioning in a short time without a Curvic (trademark) or positioning coupling. With provision of a hydraulic motor having a rotary shaft fixed to a turret head and a hollow type rotary encoder for detecting the angle of rotation of the rotary shaft, rotation of the hydraulic motor is controlled by a controller via a control valve. Locking of the rotary shaft is performed by a rebound force of a spring provided in a hydraulic cylinder by pressing a pad provided at a tip portion of a rod against a disk. Unlocking of the rotary shaft is performed by supplying a hydraulic fluid into a cylinder chamber by switching a directional control valve.