a process in which a control use actual throttle opening is computed by adding n number of times the actual throttle opening computed by the actual throttle opening computation means 10 processing in step 101 for computation of a control use actual throttle opening is executed at time intervals of 1 ms for example to enable the control use actual throttle opening computation process there are prepared n computation buffers 1 to n such as those indicated by reference numeral 301 in fig3 corresponding to the number of times the actual throttle opening is added an addition counter capable of counting the number of times the actual throttle opening is added is also prepared each operation buffer and the addition counter are first cleared to zero at the time of cpu reset in step 102 shown in the flowchart of fig2 the actual throttle opening obtained by the actual throttle opening computation processing is added in each of the operation buffers 1 to n this operation is also indicated by reference numeral 302 in fig3 in step 103 1 is added to the value in the addition counter and 1 is added n times the addition counter is clipped when the addition is repeated n times by this processing the addition counter indicating the number of times the actual throttle opening is added starts counting from zero at the time of cpu reset and is clipped when the addition is repeated n times the process thereafter advances to step 104 in which a determination is made as to whether the value in the addition counter counting the number of times the actual throttle opening is added is smaller than n if the addition counter value is smaller than n the process advances to step 105 and.