PROBLEM TO BE SOLVED: To provide a plant environment control system by which the indoor temperature of a cultivation greenhouse is properly controlled all day and night, and also the COP of a heat pump is improved.SOLUTION: The plant environment control system includes: a cultivation greenhouse 10 for cultivating plants； a heat pump 20 for reducing or increasing the indoor temperature of the cultivation greenhouse 10； air-intake switching means 35-1, 35-2 which are attached respectively to a plurality of paths through which the taken-in air of the heat pump 20 passes； a heating medium tank 40 stores heat collected with the heat pump 20 via reservation of a heat medium； a local heating means 50 locally raising the indoor temperature of the cultivation greenhouse 10 using the heat medium； and a means for controlling the destination of the taken-in air 80 activating the air-intake switching means 35-1, 35-2 to switch the destination of the taken-in air.
