A crank angle detector and an ignition timing controller comprises a rotor rotated in association with a crank shaft of an internal combustion engine and having detection portions to be detected at equivalent angle intervals in the outer circumference; and a pickup arranged in the vicinity of the outer circumference of the rotor, for generating a pulse signal when the detection portions each pass; wherein one detection portion located immediately before the crank angle corresponding to the upper dead point of a piston of the internal combustion engine, of the detection portions is set to detect a reference angle of the crank angle.