PURPOSE: To obtain an optimum desired control value of aspiration pressure and/or supercharge pressure by correcting pressure differential signals relative to the aspiration pressure and/or supercharge pressure signals and atmospheric pressure and reference pressure signals, and forming a desired value signal by adding a correction signal with the atmospheric pressure signal.

CONSTITUTION: A map 200 outputs a pressure signal PO of aspiration or supercharge pressure according to required fuel quantity and engine speed and supplies it to a junction 201 with a positive symbol. An atmospheric pressure signal PAtm or a reference pressure signal PRef are supplied with a negative symbol respectively to the junction 201 via a switch 202. A pressure differential signal dP of the two signals PAtm, PRef is outputted to a symbol step 204 and a correction step 206 from the junction 201. Then, whether or not the pressure differential signal dP is larger than zero is determined in the symbol step 204. The result is outputted to the correction step 206. In the correction step 206, a pressure differential signal dP' supplied to the junction 201 is added to the atmospheric pressure signal PAtm, and a desired pressure value signal P is outputted.