When a vehicle speed of a wheel loader (1) is determined to be not higher than a reference value (Yes) in step S4 and a forward/reverse command switch (40) is determined to have been switchingly operated (Yes) in step S5, the routine advances to step S6 where an increment ΔN of engine speed according to an engine load factor is determined. In step S7, the increment ΔN of engine speed is then added to a target engine speed Na corresponding to a depression stroke of an accelerator pedal (38), the thus-determined Na=Na+ΔN is set as a new target engine speed Na, and a target engine speed command i1 is sent to an engine controller (37).