Abstract: A detector for particulate density and the filter for trapping particulates which includes the detector includes a heat resistant insulating member and a pair of electrodes disposed on or within the surface of the filter. When the conductive particulates are attached on the heat resistant insulating member, the resistance of the member is decreased, and reversely, when the particulates are burned away from the member, the resistance is increased. Therefore, by detecting the resistance variation, the particulate density can be measured accurately and the optimum timing to refresh the filter can be determined. The detector is heat resistive, and also can detect whether the filter is completely refreshed or not. The surface of the heat resistant insulating member may be formed to be irregular so that the particulates are easily attached to the member resulting in an increase in measurement precision.