A composite device system including: a first device including a nonvolatile memory; and a second device configured to supply a power to the first device, the second device including: a power supply circuit configured to stabilize a first power supplied from an external part into a second power lower than the first power, and to supply the second power to the first device; a communication circuit configured to receive control data from the first device; and a switch configured to switch between on and off based on the control data, and to supply the first power to the first device when the switch is on, wherein the second device receives the control data from the first device by the communication circuit when data is written into the nonvolatile memory so that the switch is turned on and the first power is supplied to the first device.