To provide a program efficiently operating a boiler group when the number of combustion shiftable boilers is varied in controlling the boiler group consisting of a plurality of boilers, and to provide a controller and a boiler system.

The program for controlling the boiler group including the boilers with a plurality of stepwise combustion positions, is configured to calculate the total evaporation amount JG of the presently combustion shiftable boilers, a deviation amount PD2 between a set pressure Pmax and a present pressure PN, a ratio PR2 between the deviation amount PD2 and a control width P2 corresponding to the set pressure Pmax, and the combustion boilers and their combustion positions based on the total combustion shiftable evaporation amount JG and the ratio PR2.