The invention relates to a detecting device, in particular to a hardness detecting device of a spanner for hardware and aims to provide the time-saving and labor-saving hardness detecting device of the spanner for hardware. To achieve the objectives, the hardness detecting device of the spanner for hardware comprises a top plate, a first pull rope, a first fixed pulley, a fixing plate, a support rod, a second fixed pulley, a support, a sliding rail, a sliding block, a reel, a first bearing block, a first rotating shaft, a first gear, a first rack, a second rack, a swing rod, a thumb cylinder, a second gear, a first rotating motor, a swing plate, a first through tube, a second through tube, a support rod and the like, wherein the support rod, a first conveying device and a second conveying device are arranged on the ground from left to right sequentially. The detecting device realizes effects of being time-saving and labor-saving during detection, easy to operate, long in service life and high in stability and safety.