There is provided an art capable of detecting viable particles in a liquid and counting the number of the viable particles even if there is an influence of a Raman-scattered light by water. There are provided: a light emitting means (10) which radiates a light with a predetermined wavelength toward a liquid containing a detection target an autofluorescence selecting optical means (70) which reduces transmission of a Raman-scattered light emitted from the liquid out of lights emitted due to an interaction of the target or the liquid with the light radiated from the light emitting means (10) and transmits an autofluorescence emitted from the target and a viable particle determining means (2) which determines whether or not the target contained in the liquid is a viable particle, based on a light obtained after the Raman-scattered light is reduced by the autofluorescence selecting optical means (70), and the light emitting means (10) radiates the light with the predetermined wavelength that causes the autofluorescence and the Raman-scattered light to be different in peak wavelength.
