A power-assisted bicycle includes a torque detection mechanism system that is simple in structure, saves space, and is lightweight. A method of setting an exposure value is changed between when the luminance changing amount detected by the luminance changing amount detection unit exceeds a preset luminance changing amount and when the luminance changing amount does not exceed the preset luminance changing amount. The bilayer resist is used in the manufacture of integrated circuits. Operation is by sensing a tachometer signal from the existing distributor, ignition coil, toothed wheel or similar device that produces one electronic pulse for each cylinder cycle. The regulator further includes a balanced regulator valve applying a balancing force to offset a force of upstream pressure on a balanced valve plug. An image processing condition is set in accordance with the formed histogram to perform the image correction process for the original image.