In a crankshaft of an internal combustion engine wherein a crankthrow is shortened by the use of a multi-link mechanism, the crankthrow from the axis of a main journal to the axis of a crankpin is set shorter than one-half of a piston stroke, and an oil passage is formed to supply lubricating oil to a bearing portion of the crankpin. The pin-side opening of the oil passage, which is open at the outer peripheral surface of the crankpin, is formed in ranges other than angular ranges of 0°, 90°, 180°, and 270° with respect to a reference line extending from the axis of the main journal toward the axis of the crankpin in a decentering direction of the crankpin, thereby alleviating a stress concentration caused by a torsional torque in the vicinity of the pin-side opening of the oil passage.