An optical fiber cleaver, comprising a blade capable of applying a scratch to the outer peripheral surface of an optical fiber and a pusher pushing the optical fiber to cleave it at the scratched part, wherein it further comprises a reverse-running prevention mechanism which prevents the blade which was moved directly and gave scratch to the optical fiber from being directly moved reversely and giving scratch again to the optical fiber, the reverse-running prevention mechanism comprises a cam moved directly in connection with the blade and a cam follower being in contact with the cam and capable of directly moving the pusher, and the cam presses the pusher automatically against the optical fiber for cleavage after the optical fiber has been scratched by the blade and, after the scratch has been given completely, locked with the cam follower so as to suppress the cam from being moved directly in the reverse direction.