To control regeneration with proper timing by grasping relations between the accumulation quantity of particulates in a collecting device and traveling distance.

When travelling distance from the Nth DPF regenerating operation to the (N+1)th regenerating operation is X, a process for estimating the PM accumulation quantity is carried out several times in the travelling distance X, and the PM accumulation quantity (estimation value data)Y is accumulated. An approximation formula F, which shows relations between the travelling distance X and the PM accumulation quantity Y is computed based on distribution of the PM accumulation quantity Y. A limit PM accumulation quantity QLIM, which determines an allowable limit of PM accumulation, is used in the approximation formula F so as to obtain the travelling distance corresponding to the limit PM accumulation quantity QLIM as a non-regeneration limit travelling distance SLIM. In the case wherein the PM accumulation quantity exceeds a threshold value, PM regenerating operation is performed, and even in the case wherein the PM accumulation quantity does not achieve the threshold value and DPF regenerating operation is not performed, when the travelling distance from the last DPF regenerating operation exceeds the non-regeneration limit travelling distance SLIM, DPF regenerating operation is forcibly performed.