PURPOSE: To effectively detect the timing of watering and to take advantage of the detection for evading a failure in watering by measuring the rest of water when a water rest sensor part is stuck into the soil in the pot to proper depth.
CONSTITUTION: The dewatering detector consists of a thermometer type external case 1, the water rest sensor part 2 incorporated in the tip part of the external case 1, an index display part 3' provided to the rear end part of the external case 1, and a microcomputer 4 which is incorporated in the case 1 so that the water rest sensor part 2 is its input side and the display part is its output side. Then when the water rest sensor part 2 is stuck into the soil in the pot by the proper depth, the water rest sensor part 2 measures the rest of water. The measurement result is displayed on display parts 3 and 3'. Consequently, the timing of watering is detected effectively and utilized to evade the failure in watering.