To removably hold a tray with a simple structure by fixing a support member for the tray at the free end of a support arm, and providing a holding device arranged with an opposite piece having a guide groove on the lower face of the tray.

A circular disk 2 is fixed at the free end of a support arm 1, and a hook pin 3 is formed integrally with the disk 2. A semicircular and flat ring segment 6 is fixed to a tray 5 in response to the disk 2, and a guide groove 7 can be formed by the ring segment 6. The diameter of the guide groove 7 corresponds to the diameter of the disk 2, the tray 5 can be thrust onto the disk 2 in the nearly horizontal direction, and the segment 6 and the disk 2 are coupled in this state. A recess 9 is provided in the bottom section of the tray 5, the hook pin 3 is automatically hooked in the recess 9 when the tray 5 is thrust onto the disk 2, and the tray 5 is fixed to the disk 2.