fig5 and 6 show time series variation of the regeneration control flag fd the loading flag fl the acceleration flag fa the transient retention flag ft the opening change rate r the normal opening change rate rn or the transient opening change rate rt and the throttle opening s an explanation will be given on the throttle opening s following the time series points a to g passing successively broken lines in fig5 and 6 show the throttle opening s rt at the transient opening change rate rt and an alternate long and short dash line in fig6 shows the throttle opening s rn at the normal opening change rate rn at the point a since the regeneration control flag fd becomes 1 the regeneration control is started and the throttle opening s is reduced gradually from the normal opening sn 100 to the regeneration opening sb 30 with the normal opening change rate rn in this embodiment the normal opening sn is 100 of the opening of the intake throttle valve 20 and the regeneration opening sb is 30 of the opening of the intake throttle valve 20 at the point b since a loading request is inputted firstly in the regeneration control so that the acceleration flag fa and the loading flag fl become 1 the transient retention flag ft becomes 1 by the transient retention judgment control in the regeneration control when the engine 100.