A speaker adapted to be disposed on a head-mounted device includes a housing member, a speaker unit, a vibrating unit and an abutting member. The housing member is adapted to be disposed on the head-mounted device and is formed with an opening adapted to open toward an ear of a user when in use. The speaker unit is disposed on the housing member in a manner that the speaker unit is not directly in contact with the head of the user when in use. The vibrating unit is disposed on the housing member and is capable of generating vibrations. The abutting member is disposed on the vibrating unit, is adapted to be in contact with the skin of the user, and is capable of transmitting the vibrations to the skull of the user.