The horizontal combining unit 40 includes switches SW41, SW42, SW43, SW44, SW45 and SW46. The switch SW41 connects/disconnects the first vertical signal line VL1a with/from the first vertical signal line VL1b, and the switch SW42 connects/disconnects the first signal line VL1b with/from the first vertical signal line VL1c. The switch SW43 connects/disconnects the second vertical signal line VL2a with/from the second vertical signal line VL2b, and the switch SW44 connects/disconnects the second signal line VL2b with/from the second vertical signal line VL2c. The switch SW45 connects/disconnects the first vertical signal line VL1a with/from the first vertical signal line VL1c, and the switch SW46 connects/disconnects the second signal line VL2a with/from the second vertical signal line VL2c. The switches SW41 and SW42 correspond to the switches SWa and SWb in