PURPOSE: To simplify the structure of a transducer for detecting a command input from a control stick of aircraft and miniaturize it at the same time.

CONSTITUTION: This detection system is featured that when a command input from a control stick 2 is encoded, a light is distributed by a coupler and delayed each and fed to a slit S at each row as a multiphase optical pulse, not making them pass through the slit S of a transducer 1, while the light passed through the slit is detected by a light receiver 5, counting this light with a counter 8, through which an increase or decrease portion to a neutral position is detected, thus operation of the control stick is detected.