There are disclosed an instrument for measuring the concentration of particulates in a fluid, which is capable of determining the concentration of the particulates in the fluid with high accuracy. The instrument for measuring the concentration of the particulates in the fluid includes particulate collecting means, temperature measuring means, flow rate measuring means, impedance measuring means, time measuring means, constant determining means for determining an impedance change per unit time-particulate concentration constant from temperature and flow rate, impedance change per unit time computing means for computing the change of an impedance per unit time, and particulate concentration determining means for determining the concentration of the particulates from the change of the impedance per unit time computed by the impedance change per unit time computing means.