PURPOSE: To forecast a final angle time to be used for the time conversion of a redundant angle with a high accuracy regardless of a rotation speed difference at the time of steady rotation.

CONSTITUTION: A pulse count number and a redundant angle from the reference position of an engine rotation pulse to an objective crank angle position are sought, and when a final angle time TS1125A for the time conversion of the redundant angle is sought, a previous angle time TS1125(i-1) is sought. A difference between a rotation ascent time TN13 and a rotation lowering time TN6 in the same combustion cycle is sought as a time difference equivalent to a rotation speed change, and at the time of the steady rotation of each rotation speed NE, a time difference ΔTN after correction is carried out by conducting correction by means of a offset value A which makes the time difference substantially zero, and in addition, a final angle time TS1125A is forecasted by correcting the previous angle time TS1125(i-1) by means of the time difference ΔTN after correction. Accordingly, at the time of steady rotation, the final angle time TS1125A is forecasted uniformly and similarly.