An image sensor and an image sensing method can obtain image signals with a high S/N ratio in a high-speed image pickup operation. Signal charges are input to input transfer stage 31 of CCD memory 30. Final transfer stage 32 is formed so as to be connected to the input transfer stage 31 and able to transfer signal charges to the input transfer stage 31. In an accumulation mode, read gate 42 and drain gate 40 are not turned on and the next transfer operation of the CCD memory 30 is conducted. The accumulated signal charges are transferred on a stage by stage basis and the signal charges obtained at the first image pickup timing are transferred again straightly to the input transfer stage 31. In this state, the signal charges obtained newly at photoelectric conversion section 20 at the next image pickup timing are injected into the input transfer stage 31 by way of input gate 21. As a result of this operation, the signal charges obtained at the last image pickup timing are added to the signal charges accumulated in the input transfer stage 31 so that integrated signal charges obtained by adding the two sets of signal charges are accumulated in the input transfer stage 31.