PURPOSE: To obtain an environment recognition system between moving robots which enables the measurement of the distance between the robots and operation of communication accurately regardless of environment.

CONSTITUTION: Light beam emitted from a light emitting means 102a is admitted into a robot 100b on the side of being measured from a robot 100a on the measuring side through a reflection means 101a and the light beam emitted is reciprocated a plurality of times between reflection mean 101a and 101b between the robot 100a on the measuring side and the robot 100b on the side of being measured to input an electrical signal obtained from the light beam incident on a photodetecting means 104a into a phase comparison means 105a. A distance from the robot 100b on the side of being measured is calculated based on a phase delay value and the robot 100b on the measuring side demodulates a signal used for a modulation means 103a by a demodulation means 107b to obtain transmission information.