To perform an arithmetic operation with noise eliminated, even when a transmitting and receiving means which detects light-receiving intensity and is controlled is used under an environment in which it is easily subjected to the effect of a noise source that generates noise periodically.

At least three sections S1 to S3 to a pulse signal which is sent from a pointer and is received by a light-receiving part side and timing adjustment times t1 to t3, which are provided to be equivalent to or longer than noise generation time due to periodical pulse light emission of a fluorescent lamp are alternately provided. The amplitude of a pulse in the section where noise is not superimposed is made as a detection value. Therefore, even if noise of the fluorescent lamp is superimposed on any section of a pulse signal, the noise no longer affects the detection of amplitude intensity of a pulse.