The invention concerns a device for administering an injectable product in doses, wherein the device includes a casing, comprising a reservoir for the product, a piston, which when moved in a feed direction towards an outlet of the reservoir forces product from the reservoir, a gear rack, moving the piston in the feed direction, comprising a first series of teeth and a second series of teeth, a drive member, movable relative to the casing in and counter to the feed direction, and slaving the gear rack when moved in the feed direction, and a blocking means, arranged secured against shifting relative to the casing and cooperating with one of the series of teeth such that it prevents the gear rack from being moved counter to the feed direction and allows the gear rack to be moved in the feed direction.