PARTICLE DETECTING SENSOR

This particle detecting sensor (1) detects particles contained in a fluid of interest, and is provided with: a light projecting unit (20) which emits light (L1) toward a detection area (DA); a light receiving unit (30) which has light-receiving sensitivity with respect to the light emitted by the light projecting unit (20), and which generates and outputs an electrical signal by performing photoelectric conversion of scattered light (L2) originating from the light (L1), caused by a particle passing through the detection area (DA); a signal processing circuit (50) which, on the basis of the electrical signal, calculates a first mass concentration of a first particle category including a first particle, and a second mass concentration of a second particle category including the first particle and a second particle larger than the first particle; and a correcting circuit (60) which estimates the number of second particles on the basis of the number of first particles, and corrects the second mass concentration o