To provide a speed detecting device that can be easily mounted to a desired carrier in an existing frictional driving-type trolley conveyor and rapidly collects travel speed data of the carrier.

The speed detecting device comprises a carrier-side detecting device 21 formed by integrally interconnecting and fixing a supporting member 22 having a trolley engaging section 22a engaging with a connecting section 16 suspended between inner surfaces of right and left side plates 12 and 13 of a trolley 2, a detecting roller 23 that is mounted to the supporting member 22 and abuts on a travel rail to rotate, a position detector 24 which is connected with the detecting roller 23 and detects the rotation angle, and a transmitter 25 for radio-transmitting data according to an output of the position detector 24. The speed detecting device also comprises a fixing means for fixing the carrier-side detecting device 21 between right and left side plates 12 and 13 of the trolley 2 in a state where the trolley engaging section 22a of the supporting member 22 is engaged with the connecting section 16 suspended between inner surfaces of right and left side plates 12 and 13 of the trolley 2.