An inspection apparatus for a sheet of paper subjected to a process to impart a translucent property including a “watermark” or a “security window” includes: an inspection cylinder in which a surface facing the sheet of paper is provided with a blackened portion; IR-LED illuminators which irradiate the sheet of paper with light containing infrared rays; an IR monochrome camera which images the sheet; an IR filter which eliminates visible light in the light emitted from the IR-LED illuminators and reflected off the sheet as well as the inspection cylinder and makes only the infrared rays incident on the IR monochrome camera; and a control device which determines appropriateness of a processed portion on the sheet having the translucent property on the basis of the infrared rays emitted from the IR-LED illuminators, reflected off the sheet as well as the inspection cylinder, and made incident on the IR monochrome camera.