A bi-directional detector which enables a host and a client in a collection terminal is disclosed. The bi-directional detector includes a client detection unit in the host part, for detecting the clients connected to the host part; a client identification unit for identifying types of the clients detected by the client detection unit; a host detection unit in each of the clients for detecting the host part; and a switch unit in each of the clients for determining whether to apply comparison power to the client detection unit and the host detection unit according to whether power is applied to the client. In the bi-directional detector, the client directly detects the host part and manages the connection, thereby reducing the load on the host part, without performing a step by which a host part responds to a connection request of a client.