A wearable device includes first and second electronic modules, a connection module configured to electrically connect the first electronic module to the second electronic module, and a length adjusting module of which length is adjustable to bring the connection module in contact with a user. The length adjusting module comprises first and second fastening units configured to be assembled and disassembled and configured to be locked together in a fastened position when assembled. When the first and second fastening units are assembled, the first fastening unit is electrically connected to the second fastening unit and a length of the length adjusting module is adjusted.