PURPOSE: To immediately execute an emergency command. etc.

CONSTITUTION: A command for satellite processing is transmitted from a ground station side by attaching the execution priority order information of the command, respectively. A satellite side holds the command received from a ground station at the prescribed address of a command buffer 3. The execution priority order information attached on the command is held with a priority order generating part 4 forming a pair with the address of the buffet 3. The content held with the generating part 4 is compared with that held with a priority order register 5, and it is stored in the register 5 corresponding to an order to be executed. The address is designated from a command output part 14, and the command is read out from the buffer 3, then, it is executed. Therefore, the emergency command can be executed preferentially than another command by transmitting from the ground station side by attaching the priority order, which prevents a trouble in the operation of a satellite from occurring.