A wearable device includes a host and plural functional modules. The host includes a first housing and a controlling unit. The controlling unit includes a first electrical conduction part and a second electrical conduction part. Each functional module is capable of detachable coupling with the host. Every two adjacent functional modules are detachably coupled with each other. Each functional module includes a second housing, a functional circuit unit and a connection unit. The functional circuit unit includes a third electrical conduction part and a fourth electrical conduction part. The connection unit includes a first connection part and a second connection part. The first connection part is connected with the third electrical conduction part. The second connection part is selectively connected with the first electrical conduction part, the second electrical conduction part of the host or the fourth electrical conduction part of the adjacent function module.