A power generation planning method for use of a fuel cell device including a plurality of fuel cell units includes the step of receiving a planned power generation output value of the fuel cell device, the first determination step of determining, among the plurality of fuel cell units, the number of fuel cell units that generate power and the number of fuel cell units that do not generate power to satisfy the planned power generation output value, and the second determination step of determining the number of the fuel cell units that generate power to satisfy a value obtained by adding the total standby power of the fuel cell units that do not generate power to the planned power generation output value.