A portable digital communication apparatus includes a first housing; a second housing; a dual-axis hinge member connected to the first housing in such a manner that it can rotate about a first hinge axis and connected to the second housing in such a manner that it can rotate about a second hinge axis which is parallel to the first hinge axis to rotatably connect the first and second housings to each other; at least one coupler for connecting the dual-axis hinge member on the first and second housings; and at least one retainer positioned on the dual-axis hinge member to maintain a retaining position.