PURPOSE: To prevent acting of unnecessary load to a small animal suspended by a suspending means, by incorporating a means for adjusting the center of gravity in a peristaltic pump suspended by an L-shaped member, and adjusting the position of the center of gravity shifted during the operation of the apparatus.

CONSTITUTION: By replacing a speed reducing means 15 that has been fixed to a flange with other speed reducing means, a medical liquid is supplied from a medical liquid tank 26 to a mouse 27 at a rate determined by the speed reduction rate of the new speed reducing means. Here, if the speed reduction rate of the new speed reducing means differs from that of the previous one, the weight and the length of the speed reducing means are changed, so that the position of the center of gravity of the entire structure consisting of the speed reducing means, a motor 14 and a peristaltic pump suspended by an L-shaped member 21 is shifted. However, the position of the center of gravity is adjusted by shifting the L-shaped member 21 slightly to a hollow shaft 24 to which the L-shaped member 21 is coupled at its connecting portion 20, and then retightening an adjustment screw 19. Therefore, it is enabled to prevent acting of unnecessary load to the small animal.