The instrument is a portable non-destructive testing instrument, which can be used for the detection of the construction quality of reinforced concrete structures. It can measure the position of the steel bars on the concrete surface, detect the thickness of the steel protective layer and the diameter of the steel bars. In addition, the magnetic properties inside the concrete structure can also be The position of the body and the conductor are detected, such as the internal cable of the wall, the plumbing pipe, etc., and the detection before construction can effectively avoid damage to these facilities during construction and reduce accidents.