An image sensor has a plurality of pixels each with a photoelectric conversion element and a detection transistor the threshold voltage of which fluctuates in accordance with electrical charge generated in the photoelectric conversion element. The image sensor includes a second conductivity type shield region and a first conductivity type photoelectric conversion region; a first conductivity type well region linked to the photoelectric conversion region; a ring-like gate electrode; a second conductivity type source region at the inside of the ring-like gate electrode; a second conductivity type drain region. The image sensor further includes a potential pocket region that is formed in the well region below the ring-like gate electrode and accumulates the electrical charge, wherein the width of the gate electrode is formed narrower in the part adjacent to the photoelectric conversion region than in other parts.