Abstract: A particle counting device is improved to prevent adhesion impurities that result from condensation of condensation vapor on optical systems and the like in a particle detection area or the like of a measuring device to detect particles contained in the atmosphere or in certain gases and using condensation nuclei. In particular, in a particle measuring operation in which, in a chamber for saturated vapor that contains a liquid that can condense at a room temperature, a gas is added to a saturated vapor, the gas is introduced into a condensation part that is at a room temperature, the vapor is condensed on the particles as nuclei, and in which the particles, in a connected particle detection area, are measured, a heater is provided to keep the temperatures of the detection area, the connection pipe and the nozzle at least at a temperature higher than or equal to the temperature of the condensation part, to prevent adhesion impurities of condensation vapor on optical systems and the like in the detection area.