A microbial particle measuring apparatus includes: a light emitter configured to irradiate a fluid with light of a predetermined wavelength over a predetermined measurement time; a fluorescence receiver configured to selectively receive fluorescence emitted from particles contained in the fluid and output a signal having a magnitude corresponding to intensity of the fluorescence; a signal acquisition unit configured to obtain the signal output from the fluorescence receiver at regular intervals over the measurement time; and a determiner configured to calculate a slope of waveform of the signal obtained by the signal acquisition unit, and determine a concentration of microbial particles contained in the fluid using an attenuation amount of fluorescence intensity generated in a time period in which the slope in the measurement time is smaller than a predetermined value as an amount of attenuation derived from the microbial particles.