In an electronic device system where a controller and a target device are connected to each other via an IEEE 1394 serial bus, the controller comprises: command sending means for sequentially sending via the bus a power control command to change the power status of the target between the power-on state and the power-off state and a power status command to inquire the power status of the target device; change time calculating means for calculating power status change time needed for the target device to change the power status between the power-on state and the power-off state based on a response to the power status command that is received from the target device; and time interval determining means for determining a time interval from sending of the power control command to sending of the power status command based on the power status change time.