A crank driving device for a press designed in serial type eccentric structure. An eccentric element of crankshaft connected to a connecting rod, and an eccentric mechanism to provide a second eccentricity, are separated in the axial direction of the crankshaft. The opposite ends of crankshaft are provided, in respective eccentric holes in a pair of rotatable bodies which rotate synchronously on a basic axial line. The crankshaft is axially displaceable between a position in which it rotates in synchronism with the rotatable bodies and a position in which the crankshaft and the pair of rotatable bodies can be rotated relative to each other. The eccentricity of the device is adjusted by rotating crankshaft and pair of rotatable bodies, relative to each other, and then maintaining the relative angle of the crankshaft and the pair of rotatable bodies at constant value by connecting means after adjustment.