To facilitate the adjustment of respective parts and to make the use of a treadmill easier by stably supporting wheels by rollers for bearing an axle so that the angle between the axes of these rollers and the axis of the wheels can be adjusted and making the guiding of the wheels able to be separated from and come into contact with each other and adjustable in spacing.

A case body 1 is installed and provided with two pieces one set of the rollers 5, 5a supporting the wheels 3 respectively in supporting frames 6, 6a. The respective supporting frames 6, 6a are mounted adjustably in small- angle turning by supporting shafts 7, 7a for turning. The one end of a resistance shaft 13 is connected to the respective rollers 12, 12a of the rollers 5, 5a of the respective sets and the other end of the resistance shaft 13 is connected to the output shaft of resistors 14, 14a. The lower part of the supporting rod of the guide pieces 17, 17a of the wheels 3 is screwed to a screw rod 19 and a reduction gear rotated by a motor 20 is fitted to the screw rod 19. If the motor 20 is started, the screw rod 19 is rotated by the reduction gear and, therefore, the supporting rod screwed to the screw rod 19 moves and the attachment and detachment adjustment of the guide pieces is made possible.