A control device for an internal combustion engine, comprising: reference rotation position detection means which is configured to detect a reference rotation position of a crankshaft of the internal combustion engine; unit crank angle detection means which is configured to output a crank angle signal per unit crank angle of the crankshaft; reference crank angle cycle calculation means (203, 303) which is configured to calculate a reference crank angle cycle (TREF) indicating a time period of one cycle of the reference rotation position detected by the reference rotation position detection means; combustion period crank angle cycle calculation means (202, 302) which is configured to calculate a combustion period crank angle cycle (TPOSburn) on the basis of the crank angle signal from the unit crank angle detection means; crank angle cycle ratio calculation means (204, 304) which is configured to calculate a crank angle cycle ratio which is a ratio of the combustion period crank angle cycle (TPOSburn) and the reference crank angle cycle (TREF); and correction means (205, 305) which is configured to correct ignition timing or a fuel injection amount in accordance with the crank angle cycle ratio at a start of the internal combustion engine, wherein the combustion period crank angle cycle calculation means is configured to set a cycle having a shortest cycle of the unit crank angle in the reference crank angle cycle (TREF), as the combustion period crank angle cycle (TPOSburn); or set a cycle of the unit crank angle when a predetermined crank angle has passed from an ignition position, as the combustion period crank angle cycle (TPOSburn). reference rotation position detection means which is configured to detect a reference rotation position of a crankshaft of the internal combustion engine; unit crank angle detection means which is configured to output a crank angle signal per unit crank angle of the crankshaft; reference crank angle cycle calculation means (203, 303) which is configured to calculate a reference crank angle cycle (TREF) indicating a time period of one cycle of the reference rotation position detected by the reference rotation position detection means; combustion period crank angle cycle calculation means (202, 302) which is configured to calculate a combustion period crank angle cycle (TPOSburn) on the basis of the crank angle signal from the unit crank angle detection means; crank angle cycle ratio calculation means (204, 304) which is configured to calculate a crank angle cycle ratio which is a ratio of the combustion period crank angle cycle (TPOSburn) and the reference crank angle cycle (TREF); and correction means (205, 305) which is configured to correct ignition timing or a fuel injection amount in accordance with the crank angle cycle ratio at a start of the internal combustion engine, wherein the combustion period crank angle cycle calculation means is configured to set a cycle having a shortest cycle of the unit crank angle in the reference crank angle cycle (TREF), as the combustion period crank angle cycle (TPOSburn); or set a cycle of the unit crank angle when a predetermined crank angle has passed from an ignition position, as the combustion period crank angle cycle (TPOSburn).