Air temperatures in agriculture greenhouses may become too high in summer season for cultivating some plants. So we investigated the effects of a groundwater cooling system for the inhibition of temperature rise under high temperature conditions in a tomato cultivation plastic house. The tests were carried out from June to August 2018, in the site of Ishikawa Prefectural Agricultural Experiment Station. The main features of this research are as follows: (1) air temperatures in night-time were reduced by the interior air circulation and (2) relative humidity in day-time were increased by the mist spraying in the house.