A composite device with a high security level is provided. A composite device capable of inhibiting unauthorized use favorably is provided. The composite device includes a control portion, a detection portion, an authentication portion, and a memory portion. The detection portion has a function of detecting a touch and a function of obtaining first fingerprint data of a finger touching the detection portion. The authentication portion has a function of executing user authentication processing. The memory portion has a function of retaining second fingerprint data registered in advance. The control portion has a function of bringing a system into an unlocked state when the authentication portion authenticates a user and a function of comparing the first fingerprint data obtained by the detection portion and the second fingerprint data when the detection portion detects a touch, and bringing the system into a locked state in the case where those data do not match.