A telephone apparatus includes a telephone set consisting of a base unit and a handset removably mounted on the base unit. The apparatus also includes a transmitter/receiver, and an adaptor on which the base unit is mounted. The adaptor has an electrical connector which is electrically connected to the transmitter/receiver. The adaptor includes a main body which supports the electrical connector, and a slide member which includes a cover housing. The slide member, including the housing, is mounted on the main body for sliding movement between a first position, in which the connector is exposed for connection to the telephone set, and a second position in which the housing covers the electrical connector to protect it from dust and inadvertent impact. The main body and the slide member jointly support the telephone set with the connector connected to the telephone set, when the slide member is in the first position.