Provided is a clearance measurement device, which is a device for measuring the clearance between the inner peripheral surface of a casing and the outer peripheral surface of a rotary body. The deviceemits light having a first wavelength and light having a second wavelength toward the outer peripheral surface of the rotating body, receives reflected light from the outer peripheral surface via a first filter having a transmission band corresponding to the first wavelength, receives light via a second filter having a transmission band corresponding to the second wavelength, and measures the clearance on the basis of a time difference of the detection timing of the rotating body.