Disclosed is a swing hinge device for semi-automatically rotating a pair of facing housings of a mobile terminal on a step-by-step basis, for use in a mobile terminal having a first housing and a second housing with a display unit rotatable around a hinge axis extending in a direction perpendicular to a top surface of the first housing, the swing hinge device includes a rotation member rotatable around the hinge axis; a plate-type swing hinge member rotatably connected to the rotation member to semi-automatically rotate the rotation member on a step-by-step basis; a power supply means mounted in the swing hinge member to supply power for semi-automatically rotating the rotation member; and at least one swing locking means formed along the perimeter of the swing hinge member to lock or release the rotation member for the step-by-step interrupted rotation of the rotation member.