A cover opener for opening a cover 1a that is rotationally removed from and fixed to a reagent container 1 includes: a rotational drive unit 12 and a cover retainer 17 to retain the cover 1a by becoming engaged with a concave portion 1b provided on an upper portion of the cover 1a. A carrier 16 is driven to rotate as the rotational drive unit rotates, as well as to move in a direction of a rotational axis with respect to the rotational drive unit. Springs 19 and 20, one of which is provided between the rotational drive unit and the cover retainer, and the other between the rotational drive unit and the carrier, bias the rotational drive unit and the cover retainer or the carrier in relative fashion to move away from each other. This enables the cover of the reagent container to be reliably opened.