PURPOSE: To improve debugging efficiency by reading a conversion result from an analog/digital converter in accordance with a variable when shift to a simula tion mode is not instructed, and setting a value set based on the variable as the conversion result when the shift to the simulation mode is instructed.

CONSTITUTION: It is checked whether or not the shift to the simulation mode is instructed to the analog-digital converter 66 by referring to an externally reloadable variable corresponding to the converter at every fixed time. When no shift is instructed, the conversion result from the analog/digital converter 66 in accordance with the variable is read, and the value set based on the variable is read as the conversion result of a corresponding analog-digital converter 66 when the shift is instructed. For example, when debug is performed on a job using suction air quantity data, the conversion result of a numeric value which represents suction air quantity can be obtained by writing the numeric value which represents desired suction air quantity on a corresponding variable even without inputting the result from the suction air quantity sensor 32 to the A/D converter 66.