A docking device including a casing and an extension supporting mechanism is disclosed. The extension supporting mechanism includes a sliding member, a transmission member, a supporting member and a clamping member. The sliding member is slidably disposed on the casing. The transmission member, the supporting member and the clamping member are pivoted to the casing, respectively. The transmission member is coupled to the sliding member. The supporting member is coupled to the transmission member. The clamping member further abuts against the sliding member and is for sliding the sliding member as rotating, such that the sliding member drives the transmission to rotate. Accordingly, the transmission member is driven to activate the supporting member to stretch an extension portion of the supporting member out of the casing.