PURPOSE: To prevent connection when the positive protruded electrode of a battery is reversely inserted into the negative electrode terminal of an apparatus by providing a recess larger than the positive protruded electrode of the battery in diameter and shallower than the protruded size on the contact face of the negative electrode terminal, and arranging an insulating member on its bottom face.

CONSTITUTION: A recess 2 is provided on the contact face of a negative electrode terminal 1 with the negative electrode 6c of a battery 6, its diameter is made larger than that of a positive protruded electrode 6a, its depth is made shallower than the protruded size of the electrode 6a, and an insulating member 3 is arranged on the bottom face. When the electrode 6a is brought into contact with the insulating member 3, the terminal 1 is separated and insulated from a positive flange section 6b nearly equal to the electrode 6c in diameter because the depth of the recess 2 is made shallower than the protruded size of the electrode 6a. When the terminal 1 is made of a coil spring 1a, for example, the inner diameter of a winding end section is made larger than the diameter of the electrode 6a, and the insulating member 3 is pinched between the first winding and the second winding. When the diameter of the coil wire is made smaller than the protruded size of the electrode 6a of the battery 6, the positive flange section 6b is brought into no contact with the coil spring 1a. The reverse connection of the battery 6 is prevented, and the leakage of the battery 6 can be prevented.