To detect an object, and to determine its approach without erroneous detection.

A light signal transceiver includes: a switch SW1 between the input/output lines of an input circuit 3; and a switch SW2 between the output line of the input circuit 3 and the input line of a low-frequency component detection circuit 4. By a switch control circuit 8A, a light receiving element 2 turns on the switch SW1 for a prescribed period immediately after receiving pulsed light from a light-emitting element 1. While at least the light receiving element 2 is receiving pulsed light from the light-emitting element 1, the switch SW2 is turned off.