A 3D game machine is provided with a monitor (11) provided at a specified height position of a casing (10) for displaying images, a game control unit (100) for controlling the progress of a game, and an image control unit (110) for generating a 3D image viewed from a viewing point of a simulated camera and displacing it as a game image on a screen of the monitor (11). A transverse position and a height position of the head of a game player located in a play area before the screen of the monitor (11) are detected using one ultrasonic transmitter (31) and two ultrasonic receivers (32,33), and the viewing point of the simulated camera is so moved as to follow a displacing direction and a displacing amount of the detected position of the game player's head.