A pedal force detection mechanism for an electric-assisted bicycle, adapted to be received in a shaft housing of the electric-assisted bicycle to coordinate with a crankshaft and connect to an auxiliary power assembly, with the crankshaft movably disposed at the shaft housing, the pedal force detection mechanism comprising: a torque-transmitting member for transmitting a torque of the crankshaft unidirectionally and diverting the torque along an axial direction of the crankshaft; and a main thrust bearing for abutting against the torque-transmitting member to transmit the diverted torque; characterized by the pedal force detection mechanism further comprising: a strain sensing assembly having a strain gauge, a resilient ring-shaped base and a supporting annular base, with the supporting annular base disposed outside the torque-transmitting member and abutting against the shaft housing, allowing an axial-strain gap to be defined between the supporting annular base and the main thrust bearing, the resilient ring-shaped base being disposed outside the supporting annular base and fitted between the main thrust bearing and the supporting annular base, the strain gauge being disposed at the resilient ring-shaped base and in signal connection with the auxiliary power assembly; and a main drive gear movably disposed between the crankshaft and the shaft housing and having a main gear, an internally-connected ring body and an externally-connected ring body, the internally-connected ring body being integrally formed with the main gear and located on an inner side of the main gear, the externally-connected ring body being fixedly connected to an outer side of the main gear, wherein the torque-transmitting member and the internally-connected ring body rotate synchronously, and an axial-movement gap is defined between the torque-transmitting member and the internally-connected ring body. a torque-transmitting member for transmitting a torque of the crankshaft unidirectionally and diverting the torque along an axial direction of the crankshaft; and a main thrust bearing for abutting against the torque-transmitting member to transmit the diverted torque; a strain sensing assembly having a strain gauge, a resilient ring-shaped base and a supporting annular base, with the supporting annular base disposed outside the torque-transmitting member and abutting against the shaft housing, allowing an axial-strain gap to be defined between the supporting annular base and the main thrust bearing, the resilient ring-shaped base being disposed outside the supporting annular base and fitted between the main thrust bearing and the supporting annular base, the strain gauge being disposed at the resilient ring-shaped base and in signal connection with the auxiliary power assembly; and a main drive gear movably disposed between the crankshaft and the shaft housing and having a main gear, an internally-connected ring body and an externally-connected ring body, the internally-connected ring body being integrally formed with the main gear and located on an inner side of the main gear, the externally-connected ring body being fixedly connected to an outer side of the main gear, wherein the torque-transmitting member and the internally-connected ring body rotate synchronously, and an axial-movement gap is defined between the torque-transmitting member and the internally-connected ring body.