Disclosed are an apparatus and method for converting 2D input image signals into 3D stereoscopic image signals and outputting the converted 3D stereoscopic image signals. According to a method of converting image signals according to an embodiment of the present inventive concept, first, motion information about a current frame that is 2D input image signals is acquired, and then a motion type of the current frame is determined using the acquired motion information. As a result of the determination, if the motion type of the current frame is a horizontal motion frame, it is determined whether the current frame is a scene change frame. If the current frame is the horizontal motion frame and is not the scene change frame, 3D output image signals are generated using a current image and a delayed image. If the current frame is not the horizontal motion frame, or if the current frame is the horizontal motion frame and the scene change frame, a depth map is applied to the current image and 3D output image signals are generated. In this case, the depth map is acquired using the horizontal boundary and a difference in a sense of depth according to a vertical location to embody a stereoscopic image.