A particulate matter concentration measuring apparatus configured to measure concentration of particulate matter in exhaust gas passing through an exhaust line includes an exhaust gas collecting line branched from the exhaust line, a particulate matter detection filter provided in the exhaust gas collecting line, a differential pressure sensor configured to sense differential pressure between an inlet and an outlet of the particulate matter detection filter, a passage wall disposed so that the exhaust gas flows to a downstream side of the particulate matter detection filter, an inlet side passage through which the exhaust gas flows into the particulate matter detection filter in the passage wall, and an outlet side passage through which the exhaust gas flows out from the particulate matter detection filter. The outlet side passage has an outlet side cross-sectional area approximately 1.0 times or more larger than an inlet side cross-sectional area of the inlet side passage.