PURPOSE: To make much an exhaust circulation that produces no low temperature corrosion attainable, by performing the exhaust circulation only the duration of up to the elapse of the specified time from the start of idling according to engine temperature in time of idling, while in xases other the above, performing the exhaust circulation with a flow rate commensurate to engine load.

CONSTITUTION: In time of engine operation, at a control unit 40, first a fact of whether or not an engine 1 is operated for idling is discriminated on the basis of the output of a pedaling quantity sensor 41, and when 'YES' is the case, exhaust gas circulation (EGR) time and EGR flow both are determined according to the cooling water temperature detected at a water temperature sensor 43. That is to say, when the cooling water temperature is above the specified value (for example, 70deg), a suction pressure regulating valve 29 is controlled so as to cause both the EGR time and the EGR flow to be increased in a continuous or staged manner in proportion to a rise in the temperature. On the other hand, when 'NO' is the case, the suction pressure regulating valve 29 is controlled with the control signal determined on the basis of each output signal of the pedaling quantity sensor 41 and the engine speed sensor 42, thus the opening of an EGR control valve 11 is controlled.