PURPOSE: To make the replacement of a battery easy, by attaching and detaching a battery cover through the shaking of seesaw movement for a middle point of the battery cover around a fulcrum formed on a main body.

CONSTITUTION: A cylindrical projection 9a is inserted in a long-hole recess 2a provided to both side walls 2b of an upper case 2 in one end of a battery cover 9. A semicircular projection 9d of a pawl 9c of other end of the cover 9 is fallen to a recess 3a of triangle cross section formed at the inside of a lower case 3 to contain a battery 8 in a main body. A semicircular projection 2d is formed to the upper case 2 at almost middle part between the pawl 9c and the projection 9a. In pushing one end 9h of the cover 9, the cover is shaken by taking the projection 2d as a fulcrum and the pawl 9c of the other end is sprung up. The battery 8 can completely be replaced by touching a finger to a tip lower surface 9i and opening it through pushing up. Thus, the battery can be replaced simply without using a tool.