The present invention relates to a particle measuring method for irradiating light to a surface of a substrate to scatter the light so as to measure a condition of particles on the substrate based on the scattered light. The particle measuring method according to the present invention comprises the steps of: heating a certain liquid to obtain a steam; supplying the steam onto a substrate so that a content of the steam is absorbed by each particle, while a temperature of the substrate is maintained in such a manner that the steam does not condense on the substrate; cooling the substrate before the particle dries so that the content absorbed by the particle is solidified, while preventing generation of solidified substance on regions of the surface of the substrate to which no particle adheres; and irradiating light to the substrate to scatter the light and detecting the scattered light, under a condition in which the content absorbed by the particle has been solidified.