A compression autoignition engine configured to control compression autoignition by ignition in a combustion chamber , and comprising: an injector mounted to the engine and configured to inject fuel to be supplied into the combustion chamber ; a spark plug disposed so as to face an inside of the combustion chamber , and configured to ignite air-fuel mixture in the combustion chamber ; and a controller connected to the injector and the spark plug and configured to operate the engine by outputting control signals to the injector and the spark plug , wherein the controller is configured to control the injector so that fuel is injected by a plurality of divided injections in a compression stroke, and thereafter, output a control signal to the spark plug at predetermined ignition timing so that, by ignition, unburned air-fuel mixture in the combustion chamber combusts by autoignition, and the controller is configured to perform control so that, when load on the engine is high, an amount of fuel injected at later timing among the plurality of injections becomes larger than when the load is low, characterized in that the controller is configured to calculate an estimated value of a state quantity in the combustion chamber after closing an intake valve , and configured to set each of an amount of injection in the plurality of injections based on the estimated value of the state quantity, and the controller is configured to read change of a pressure in the combustion chamber detected by a pressure sensor (SW6), configured to determine, based on the change of the pressure in the combustion chamber , a combustion state of the air-fuel mixture in the combustion chamber , configured to compare a result of detection of the combustion state with the estimated value of the state quantity, configured to calculate an error between the estimated value of the state quantity and an actual state quantity, and configured to use the calculated error to calculate an estimated value of the state quantity in the combustion chamber , subsequently. an injector mounted to the engine and configured to inject fuel to be supplied into the combustion chamber ; a spark plug disposed so as to face an inside of the combustion chamber , and configured to ignite air-fuel mixture in the combustion chamber ; and a controller connected to the injector and the spark plug and configured to operate the engine by outputting control signals to the injector and the spark plug , wherein the controller is configured to control the injector so that fuel is injected by a plurality of divided injections in a compression stroke, and thereafter, output a control signal to the spark plug at predetermined ignition timing so that, by ignition, unburned air-fuel mixture in the combustion chamber combusts by autoignition, and the controller is configured to perform control so that, when load on the engine is high, an amount of fuel injected at later timing among the plurality of injections becomes larger than when the load is low, characterized in that the controller is configured to calculate an estimated value of a state quantity in the combustion chamber after closing an intake valve , and configured to set each of an amount of injection in the plurality of injections based on the estimated value of the state quantity, and the controller is configured to read change of a pressure in the combustion chamber detected by a pressure sensor (SW6), configured to determine, based on the change of the pressure in the combustion chamber , a combustion state of the air-fuel mixture in the combustion chamber , configured to compare a result of detection of the combustion state with the estimated value of the state quantity, configured to calculate an error between the estimated value of the state quantity and an actual state quantity, and configured to use the calculated error to calculate an estimated value of the state quantity in the combustion chamber , subsequently. <EOS>