Providing an optical sensor, an optical temperature measuring device, and a measuring method of using the optical sensor, which improves the resolving ability of thermometric distance in low price without speeding up a sampling frequency or pulse width. The optical sensor has: a sensing portion having an optical fiber to be disposed at a measurement point of temperature, distortion, pressure etc.; a light source to output a light to the sensing portion; and a photodetector to detect a backscattered light from the sensing portion; the sensing portion has a tape sheet and the optical fiber shaped into a corrugated form with a predetermined curvature.