Abstract: Impact instrument for joining prosthetic implants, comprising a housing which accommodates a striker pin, a first spring element associated with the striker pin, a release device and, at least in part, a striking piece, wherein the striking piece projects from the housing at an end face, wherein the release device is movable between a fixing position and a release position, wherein the striker pin is spaced apart from the striking piece the fixing position, wherein the release device moves automatically from the fixing position to the release position when the striking piece moves axially into the housing, in order to release the striker pin once the release position has been reached, so that the latter moves in the direction of the striking piece, accelerated by the first spring element.