An image sensor, comprising: a plurality of pixel units each of which includes pixel circuitry and a reset transistor, wherein the pixel circuitry includes a photoelectric converting unit that performs photoelectric conversion on light of a certain color incident through a color filter and a transfer transistor that transfers charges obtained by the photoelectric conversion of the photoelectric converting unit and is controllable for each color, the reset transistor connects the transfer transistor to an analog to digital converting unit that performs AD conversion, and resets the charges, and according to control of the transfer transistor, the charges are read from the photoelectric converting unit through the transfer transistor and the reset transistor, and a voltage corresponding to the charges is supplied to the AD converting unit connected to the reset transistor, wherein as the transfer transistor is controlled for each color, the voltage corresponding to the charges is supplied to the AD converting unit for each color, wherein the AD converting unit is connected to a power line that connects a drain of the reset transistor with a power source, wherein the image sensor further comprises a conversion control unit that causes the power line to enter a floating state, causes the charges to flow to the power line in the floating state through the reset transistor, converts the charges to a voltage, and supplies the voltage to the AD converting unit connected to the power line, wherein the conversion control unit includes a step-down unit that generates a stepped-down voltage obtained by stepping down a voltage of the power source, and the conversion control unit applies the stepped-down voltage to the power line connected with the reset transistor in the on state, and then causes the power line to enter the floating state. a plurality of pixel units each of which includes pixel circuitry and a reset transistor, wherein the pixel circuitry includes a photoelectric converting unit that performs photoelectric conversion on light of a certain color incident through a color filter and a transfer transistor that transfers charges obtained by the photoelectric conversion of the photoelectric converting unit and is controllable for each color, the reset transistor connects the transfer transistor to an analog to digital converting unit that performs AD conversion, and resets the charges, and according to control of the transfer transistor, the charges are read from the photoelectric converting unit through the transfer transistor and the reset transistor, and a voltage corresponding to the charges is supplied to the AD converting unit connected to the reset transistor, wherein as the transfer transistor is controlled for each color, the voltage corresponding to the charges is supplied to the AD converting unit for each color, wherein the AD converting unit is connected to a power line that connects a drain of the reset transistor with a power source, wherein the image sensor further comprises a conversion control unit that causes the power line to enter a floating state, causes the charges to flow to the power line in the floating state through the reset transistor, converts the charges to a voltage, and supplies the voltage to the AD converting unit connected to the power line, wherein the conversion control unit includes a step-down unit that generates a stepped-down voltage obtained by stepping down a voltage of the power source, and the conversion control unit applies the stepped-down voltage to the power line connected with the reset transistor in the on state, and then causes the power line to enter the floating state.