Crank device with labor-saving mechanism and bicycle crank assembly

The invention relates to a crank device with a labor-saving mechanism and a bicycle crank assembly, the crank device comprises a crank mechanism, a transmission mechanism, a supporting assembly and a rotary arm assembly, and the crank mechanism comprises a crank, a shaft end gear and a pedal end gear; the transmission mechanism comprises a rotating shaft, a first gear and a second gear. Annular grooves are formed in the two ends of the rotating shaft. The supporting assembly is connected to the rotating shaft in a sleeving mode and comprises an outer ring and balls, and the balls are contained in the annular grooves and clamped between the rotating shaft and the outer ring. The rotating arm assembly comprises a first rotating arm and a second rotating arm, one end of the second rotating arm is connected with the first rotating arm, and the other end of the second rotating arm is connected with the pedal end gear. Therefore, the transmission stability can be improved, and the service life can be prolonged. 本申请