[Problem] To provide a component measuring device in which an insertion/extraction opening for a test medium is protected and yet which is excellent in operability. [Solution] A component measuring device 100 configured so that the amount of glucose components contained in blood (blood glucose level) is measured using a test medium T having the blood of a user adhered thereto, said component measuring device 100 comprising a casing 10, a cover member 20 which is integrally provided with the casing so as to be rotatable with respect to the casing 10 and approachable thereto and separable therefrom, and a medium mounting part 30 which is provided on a surface of the casing 10 and has an opening 31 through which the test medium T is inserted and extracted. The cover member 20 is configured so as to rotate between a protection position, which is a first position for covering the opening 31, and an eject operation position, which is a second position disposed on the opposite side to the protection position in the casing 10.