To improve the efficiency of a self-ignition internal combustion reciprocating piston-engine in order to suppress the production of NOx gas and to operate the engine much more economically.

At least one state variable of an internal combustion reciprocating piston-engine is measured using a sensor 10. Further, the start of a fuel injection device 3 and the start of at least either one of opening and closing of an intake valve 5 or an exhaust valve 4, are adjusted so that the compression pressure in a combustion chamber as a function of load in the upper load area, becomes constant or almost constant, based on at least one state variable above mentioned.