Power assist device for bicycle, and bicycle

An electric power assist device for bicycles, wherein a bicycle is provided with a crankshaft configured to be driven by a pedaling force transmitted from a pedal via a crankarm, the electric power assist device comprising:

• an electric motor connected to the crankshaft or the crankarm of the bicycle in a torque transmitting relationship;
• and
• a control unit configured to control the electric motor,
• wherein the control unit comprises:
• a pedaling force estimator configured to estimate a pedaling force put on each pedal of the bicycle based on a variation between measurements measured at a first crank rotational angle and a second crank rotational angle which is different from the first crank rotational angle, the measurements being indicative of at least one of a current level flowing in the electric motor, an angular velocity level of the crankshaft, and an angular acceleration level of the crankshaft;
• a crank rotational angle adjuster configured to adjust at least one of the first crank rotational angle and the second crank rotational angle according to at least one of a gradient level of a road on which the bicycle is traveling, a velocity level of the bicycle, an angular velocity level of the crankshaft, and an angular acceleration level of the crankshaft;
• and
• a motor drive controller configured to control the electric motor based on the pedaling force estimated by the pedaling force estimator.