A target engine torque (dTE) after an environmental correction is calculated by interpolating it between an environmentally corrected maximum engine torque (temax#) and an environmentally corrected minimum engine torque (temin#) such that a ratio (k) of a nominal target engine torque between a nominal maximum engine torque and a nominal minimum engine torque under a predetermined environmental condition becomes essentially equal to a ratio of the target engine torque (dTE) between the environmentally corrected maximum engine torque (temax#) and the environmentally corrected minimum engine torque (temin#). The environmentally corrected maximum engine torque (temax#) is obtained by multiplying the nominal maximum engine torque (temaxb) and a correction coefficient (Ke) according to the environmental condition together.