Provided are an image pickup device and a camera system that are capable of performing high-precision image pickup with less noise both at low illuminance and high illuminance without increasing the speed of a sense circuit and power consumption. The image pickup device includes a pixel array section including a plurality of pixels arranged in an array, each of the pixels including a photoelectric conversion device, a storage section, and an amplifier device configured to output an accumulated charge as an electrical signal, each of the pixels configured to output an electrical signal to an output signal line in response to photon incidence; and a sense circuit section including a sense circuit, the sense circuit configured to perform decision as to whether or not a photon is incident on the pixel in a predetermined period, in which the sense circuit includes an AD conversion device connected to the output signal line, the AD conversion device is allowed to operate by at least two modes, i.e., a one-bit output mode by binary decision and a gray-scale output mode by multi-bit resolution, and at least when the one-bit output mode is selected, the AD conversion device integrates output results from each of the pixels by a plurality of exposures to determine intensity of light incident on each of the pixels by calculation.