The vertical control unit 70 (see FIG. 6) sets both the switch SWa and the switch SWb in the horizontal combining unit 40 in an ON state. In addition, the vertical control unit 70 reads out a pixel signal from a pixel 10E at the central position among the three× three=nine pixels, to the second vertical signal line VL2b. The vertical control unit 70 also reads out pixel signals from the eight pixels, i.e., pixels 10A through 10D and pixels 10F through 10I, located around the central pixel 10E, to the first vertical signal lines VL1. To describe this in more specific detail, the vertical control unit 70 reads out the pixel signals from the pixels 10A, 10B and 10C in the first column to the first vertical signal line VL1a, reads out the pixel signals from the pixels 10D and 10F in the second column to the first vertical signal line VL1b and reads out the pixel signals from the pixels 10G, 10H and 10I in the third column to the first vertical signal line VL1c. As a result, the pixel signals from the pixels 10A, 10B and 10C in the first column are combined and a combined pixel signal is generated on the first vertical signal line VL1a, whereas the pixel signals from the pixels 10D and 10F in the second column are combined and a combined pixel signal is generated on the first vertical signal line VL1b. Likewise, the pixel signals from the pixels 10G, 10H and 10I in the third column are combined and a combined pixel signal is generated on the first vertical signal line VL1c.
