To provide a method for controlling the culture medium temperature of a plant cultivation bed, for greatly decreasing feeding facility cost and running cost by properly controlling feeding to a heating wire laid in the culture medium of a cultivation bed.

A culture medium temperature control system 40 of a culture bed 3 of an elevated cultivation device 1 for strawberry cultivation controls the culture medium temperature to be temperature within a setting permissible zone by dividing a feeding system to each of heating wire tapes 31 and 32 laid on each of the cultivation beds 3 into a plurality of electrothermal body feeding systems st1-st8, and performing time-sharing feeding operation to each of the electrothermal body feeding systems st1-st8 in a specified time zone including a midnight electricity zone to which midnight electric utility charge during a day is applicable.