A control device for controlling a power supply device that supplies power to a work machine includes a load amount acquisition unit configured to acquire load information indicating a load amount of the work machine during a work period of the work machine, and an output condition determination unit configured to determine an output rate of a fuel cell based on the load amount indicated by the load information during the work period. The power supply device includes the fuel cell. The work period may be a period starting when information indicating start of work of the work machine is received and ending when information indicating end of the work of the work machine is received.