A thickness detection device for sheet-type medium includes a fixing frame, a reference shaft and a detection assembly shaft. A reference roller is fixedly sleeved on the reference shaft. At least one detection roller is provided on the detection assembly shaft, and the detection roller is in an elastic contact with the reference roller. The detection roller is sleeved on the detection assembly shaft by a bracket, the bracket has an elongated hole through which the bracket is sleeved on the detection assembly shaft, an elastic element is provided between an end of the elongated hole and the detection assembly shaft, and the elastic element enables the detection assembly shaft to elastically maintain a certain distance from the end of the elongated hole. Thus, thickness signal obtained is not interfered by banknote displacements in other directions, and thickness detection of the full banknote can be achieved.