A component measuring apparatus is provided with a case having a cylindrical case main body and a cover arranged to cover the base end opening section of the case main body; a chip mounting section for mounting a chip; a light measuring section for detecting a prescribed component; a printed board whereupon a control section having a function of controlling the operation of the light measuring section is arranged; a liquid crystal display device; a battery arranging section for arranging a battery provided on the cover; an 0-ring arranged between the case main body and the light measuring section on the leading end section of the case main body; and an 0-ring arranged between the case main body and the cover on the base end opening section of the case main body. Sealing of inside the case is ensured by the 0-ring.
