In order to calculate an estimation of the quantity of accumulated particulates in a filter (32), a first estimation calculation unit (100) that outputs first estimation data (XA) calculated from the filter before and after differential pressure, and a second estimation calculation unit (110) that outputs second estimation data (XB) based on the engine operation status. Of the first and second estimation data (XA, XB), the estimation data having the higher dependability, as viewed from the engine speed at that time, is selected, whether or not to regenerate the filter is determined and with the differential between the first and second estimation (XA, XB) also taken into consideration, when the differential is larger than a prescribed value, even if the engine speed is high, the first estimation data XA is not selected since there is a risk that the dependability of the estimation value is low due to cracking of the accumulated particulates.