A Hall detection device for a thickness of a sheet medium is provided, including a mounting rack, a reference shaft and a floating wheel assembly, wherein the floating wheel assembly includes a bracket and at least one floating wheel, one end of the bracket being mounted on the mounting rack via a floating wheel rotary shaft and the other end thereof being rotationally fitted with the floating wheel so as to form a free end, a torsional spring is provided between the floating wheel rotary shaft and the bracket so that the floating wheel elastically bears against the reference shaft, and the bracket is fixedly mounted with a detection block and a sensor for detecting a displacement amount of the detection block.