A control apparatus of an internal combustion engine including combustion state control means for switching a spark ignition combustion mode in which an air-fuel mixture is spark-ignited by means of an igniter and a compression ignition combustion mode in which the air-fuel mixture is self-ignited by piston compression, comprising: operation area setting means which is a spark ignition operation area/compression ignition operation area setting map memory part for previously setting in accordance with operation conditions a spark ignition operation area in which the engine is operated in the spark ignition combustion mode, and a compression ignition operation area in which the engine is operated in the compression ignition combustion mode, wherein said operation area setting means further for setting in accordance with operation conditions a switching stable area set within the compression ignition operation area in which switching of combustion from the spark ignition combustion mode to the compression ignition combustion mode is allowed; and combustion mode selection means for selecting the spark ignition combustion mode when the operation conditions fall within the spark ignition operation area set by the operation area setting means and selecting the compression ignition combustion mode when the operation conditions fall within the switching stable area set by the operation area setting means in operation of the spark ignition combustion mode; wherein in the compression ignition combustion mode, the control apparatus is configured to perform compression ignition combustion by a two-stroke operation, characterized in that the control apparatus is configured to continue the compression ignition combustion mode as long as the operation conditions fall within the compression ignition operation area upon operation by the compression ignition combustion mode. operation area setting means which is a spark ignition operation area/compression ignition operation area setting map memory part for previously setting in accordance with operation conditions a spark ignition operation area in which the engine is operated in the spark ignition combustion mode, and a compression ignition operation area in which the engine is operated in the compression ignition combustion mode, wherein said operation area setting means further for setting in accordance with operation conditions a switching stable area set within the compression ignition operation area in which switching of combustion from the spark ignition combustion mode to the compression ignition combustion mode is allowed; and combustion mode selection means for selecting the spark ignition combustion mode when the operation conditions fall within the spark ignition operation area set by the operation area setting means and selecting the compression ignition combustion mode when the operation conditions fall within the switching stable area set by the operation area setting means in operation of the spark ignition combustion mode; wherein in the compression ignition combustion mode, the control apparatus is configured to perform compression ignition combustion by a two-stroke operation, characterized in that the control apparatus is configured to continue the compression ignition combustion mode as long as the operation conditions fall within the compression ignition operation area upon operation by the compression ignition combustion mode.