A plant growing device 1 is provided with a ventilation unit 6 including an intake unit 61 for taking the air into a growing chamber R and an exhaust unit 62 for exhausting the air from the growing chamber R. The ventilation unit 6 operates in either an intake/exhaust mode for taking the air into and exhausting the air from the growing chamber R or a circulation mode in which the air is circulated in the growing chamber R. By switching between these two modes, CO2 is taken into the growing chamber R and gas concentration, a temperature, and a humidity in the growing chamber R become uniform, leading to an improvement of the growing efficiency of plants P.
