Electronic Control Device and Combustion State Detection System

A rotation speed or a rotation time of a crankshaft at a certain angle is calculated on a basis of a change in a detection signal of a sensor of the crankshaft. Then, when a combustion cylinder is switched, information on the rotation speed or the rotation time for at least two combustion cycles is obtained, and a combustion phase is calculated on the basis of the rotation speed or the rotation time. Accordingly, by using the that measures rotation of the crankshaft, it becomes possible to detect a combustion state of the internal combustion engine with high accuracy.