To attain early regulation of a gap between dies by improving measuring precision of the thickness of a sheet-like member, attaining pressure resistance and explosion-proof structure of measuring constitution equipment including a radiation source, furthermore, enabling measurement of sheet thickness just after sheet molding regardless of the shape of the molded sheet-like member.

A thickness measuring system properly arranges an X ray source 1 (radiation source), an X ray detector 2 (radiation detector), a Ti plate 6 (characteristic X ray generating substance) for generating a characteristic X ray having peculiar energy when irradiating an X ray. The thickness measuring system calculates the thickness of a sheet S on the basis of an attenuation amount of intensity of the characteristic X ray incident on the X ray detector 2 by irradiating the Ti plate 6 with the X ray emitted from the X ray source 1, being generated with the Ti plate 6 by irradiation and transmitting the sheet S (member to be measured).