A start control device of an internal combustion engine capable of realizing a more efficient start control of the engine by recognizing the absolute angle of an engine crank shaft, wherein the absolute angle of the crankshaft (13) is calculated based on the ignition reference signal of the engine and the commutation position pulse signal of a starter motor (10) and the starter motor (10) is controlled based on the absolute angle. The starter motor (10) is rotated reversely based on the calculated absolute angle, and rotated forwardly to start the engine after the crankshaft (13) is temporarily rotated reversely to an expansion stroke, whereby, because the timing of the crankshaft (13) from reverse to forward rotation is controlled accurately by the absolute angle to enable an efficient engine start control, an efficient inertia start control can be realized, and the absolute angle of the crankshaft (13) of the engine can be recognized accurately by a crank angle detector without increasing the number of reluctors (40).