PROBLEM TO BE SOLVED: To provide an automatic irrigation system that can avoid competition between insolation irrigation and regularly-scheduled irrigation to carry out proper irrigation without scheduling inhibition time.SOLUTION: A CPU 100 in a microcomputer 10 executes an irrigation control program 112 in a program memory 110 for integrating insolation irrigation points Ps and regularly-scheduled irrigation points Pt every second to determine a total integration value S. When the total integration value S reaches a threshold value "1," the CPU 100 outputs a control signal to relay circuits 52A to 52D. Then the relay circuits 52A to 52D turn ON and power is supplied to solenoid valves 50A to 50D from a power source 60 to "open" the solenoid valves 50A to 50D. Thus water or liquid fertilizer is supplied from tanks 70A to 70D to sprinklers 80A to 80D to conduct irrigation in farm fields 90A to 90D.
