To gauge the thickness of an object to be gauged with high precision by improving economy and maintainability.

This thickness gauging device, which gauges the thickness of an object 1 to be gauged which is carried by the rotational movement of a roller 2b rotating around a rotating shaft, is provided with a distance gauging means 3 that is mounted above the roller 2b, and gauges a distance to the roller 2b or the object 1 to be gauged by irradiating the light 7 in the roughly vertical direction to the conveyance direction of the object 1 to be gauged and detecting the reflected light 8 of the light 7, and a calculating means 11 that determines the thickness of the object 1 to be gauged based on a distance to the object 1 to be gauged by the distance gauging means 3, and a distance to the roller 2b gauged by the distance gauging means 3.