A radiation image sensor comprising: a charge generation section absorbing radiation to generate charge; and a circuit board accumulating and transferring the charge generated in the charge generation section, wherein the charge generation section is disposed on the circuit board, wherein the circuit board includes: a semiconductor substrate; a capacitive section accumulating the charge generated in the charge generation section; and a MOS transistor in the semiconductor substrate, the MOS transistor including one end connected to the capacitive section and another end connected to a wire transferring the charge, wherein each of the one end and the another end are impurity diffused regions, and wherein the capacitive section includes a partial region of the semiconductor substrate, a conductor layer disposed on the partial region and electrically connected to the charge generation section, and an insulating layer interposed between the partial region and the conductor layer, characterised in that an upper surface of the conductor layer is electrically connected with the one end of the MOS transistor through intra-layer and inter-layer wiring disposed on the semiconductor substrate, wherein the capacitive section further includes an additional impurity diffused region (12c, 12d) in which an impurity to impart a conductivity type different from a conductivity type of the semiconductor substrate is diffused, the additional impurity diffused region being located next to the partial region of the semiconductor substrate, wherein the additional impurity diffused region (12c, 12d) and the conductor layer are electrically connected to each other. a charge generation section absorbing radiation to generate charge; and a circuit board accumulating and transferring the charge generated in the charge generation section, wherein the charge generation section is disposed on the circuit board, wherein the circuit board includes: a semiconductor substrate; a capacitive section accumulating the charge generated in the charge generation section; and a MOS transistor in the semiconductor substrate, the MOS transistor including one end connected to the capacitive section and another end connected to a wire transferring the charge, wherein each of the one end and the another end are impurity diffused regions, and a semiconductor substrate; a capacitive section accumulating the charge generated in the charge generation section; and a MOS transistor in the semiconductor substrate, the MOS transistor including one end connected to the capacitive section and another end connected to a wire transferring the charge, wherein each of the one end and the another end are impurity diffused regions, and wherein the capacitive section includes a partial region of the semiconductor substrate, a conductor layer disposed on the partial region and electrically connected to the charge generation section, and an insulating layer interposed between the partial region and the conductor layer, characterised in that an upper surface of the conductor layer is electrically connected with the one end of the MOS transistor through intra-layer and inter-layer wiring disposed on the semiconductor substrate, wherein the capacitive section further includes an additional impurity diffused region (12c, 12d) in which an impurity to impart a conductivity type different from a conductivity type of the semiconductor substrate is diffused, the additional impurity diffused region being located next to the partial region of the semiconductor substrate, wherein the additional impurity diffused region (12c, 12d) and the conductor layer are electrically connected to each other.