To realize highly accurate noncontact measurement of spinning speed of a bullet by measuring the spinning speed based on a sine wave signal produced from a photoelectric element depending on the spinning speed of a bullet being accelerated while spinning in a gun barrel.

A laser light 5 emitted from a laser light source 3 transmits through a first polarization plate 4 fixed to a bullet 1 and reflected on a mirror 6 disposed at the tip of the muzzle of a gun 2a. A reflected laser light 5 transmits through a second polarization plate 7 and an optical filter 8 before being received by a photoelectric element 9 and a sine wave signal 9a therefrom is recorded on a data recorder 10. The recorded data is processed and converted into a spinning speed. Output from the photoelectric element 9 is minimized when the polarization plate 4 is orthogonal to the polarization angle of the polarization plate 7 and minimized when they are aligned. Consequently, an output waveform comprising the sine wave signal 9a of the photoelectric element 9 is obtained every time when the bullet 1 spins by 90° and a peak output appears. According to the arrangement, spinning speed can be detected at the time of shooting the bullet 1.