Embodiments of the present invention may provide a PET-MRI hybrid system capable of arranging a PET apparatus and an MRI apparatus in a line. An MRI room containing the MRI apparatus and a PET room containing the PET apparatus are provided at either side of a central waiting room as opposed to each other about the waiting room. A rail portion linearly extends from the PET room to the waiting room on their bottoms. Another rail portion linearly extends on the bottom of the MRI room. A transfer unit, which supports a subject lying thereon, travels along the rail portions of the waiting room, the MRI room and the PET room. A bridge unit is provided between the rail portion of the waiting room and the rail portion of the MRI room. The bridge unit provides a space for opening and closing a shield door of the MRI room and allows the transfer unit to be reciprocated between the waiting room and the MRI room by selectively connecting the rail portion of the waiting room and the rail portion of the MRI room.