PURPOSE: To supply a constant striking energy on a drop surface, by keeping an object to be dropped, in which a weight is placed in a hollow inside while the weight thereof is made variable, at a fixed height with a stopper.

CONSTITUTION: When dropping an object 2 to be dropped, the other end of a stopper C5 is pressed to a body 1 against a spring force of a plate spring 6 to release the engagement between a stopper A3 and the stopper C5, causing the object 2 being dropped to drop to a drop surface 7. Then, the body 1 is reversed in rotation to retain the dropped object 2 with a stopper E9 and the object can be returned to the original position by reversing the body 1 again. The object 2 being dropped is made hollow inside and the weight thereof can be changed by varying the weight of the weight 10 set inside thereof.