To provide a flow rate detection device, capable of detecting the flow rate of oil flowing inside a pipe by utilizing a granularly flowing state of oil in a bent part of the pipe.

This device comprises a light-emitting element 21 irradiating the bent part Pc formed in the translucent pipe P with light; a light-receiving element 22 for receiving the light emitted from the light emitting element 21 and transmitted through the bent part Pc of the pipe P, and outputting a signal corresponding to the light-receiving quantity; a detection signal generation unit 100 for generating a detection signal changing, corresponding to existence of oil particles of the oil flowing granularly in the bent part Pc of the pipe P based on the signal from the light-receiving element 22; a pulse counter 201 for counting each part, corresponding to existence of oil particles of the detection signal generated by the detection signal generation unit 100; and an arithmetic operation part 205 generating flow rate information, based on the counted value obtained by the pulse counter 201.