A storage medium stores a control program including program code for, in the case of increasing a quantity of combustion in the boiler group, after a high-efficiency combustion shift signal that makes the shift to the high-efficiency combustion position is output to all of the boilers subject to high-efficiency control by which control is conducted on the basis of combustion at the high-efficiency combustion position, outputting a control signal that makes the shift to a higher combustion position than the high-efficiency combustion positions for any one of the high-efficiency control subject boilers.