An OCT device comprising: a light source outputting light; a splitting unit outputting first split light and second split light by splitting the light output from the light source; a probe unit irradiating a measurement target object with the first split light output from the splitting unit and inputting and guiding light from the measurement target object; a coupling unit inputting light guided by the probe unit and reached as sample light, inputting the second split light output from the splitting unit and reached as reference light, and multiplexing the input reference light and the input sample light, and outputting an interference light caused by multiplexing; and a photodetector detecting an intensity of the interference light output from the coupling unit, wherein the photo detector comprises: a silicon substrate comprised of a semiconductor of a first conductivity type, having a first principal surface and a second principal surface opposed to each other, and having a semiconductor region of a second conductivity type formed on the first principal surface side; and a transfer electrode part provided on the first principal surface of the silicon substrate and transferring a generated charge, wherein in the silicon substrate, an accumulation layer of the first conductivity type having a higher impurity concentration than the silicon substrate is formed on the second principal surface side and an irregular asperity is formed in a region opposed to at least the semiconductor region of the second conductivity type, in the second principal surface, and wherein the region in which the irregular asperity is formed in the second principal surface of the silicon substrate is optically exposed. a light source outputting light; a splitting unit outputting first split light and second split light by splitting the light output from the light source; a probe unit irradiating a measurement target object with the first split light output from the splitting unit and inputting and guiding light from the measurement target object; a coupling unit inputting light guided by the probe unit and reached as sample light, inputting the second split light output from the splitting unit and reached as reference light, and multiplexing the input reference light and the input sample light, and outputting an interference light caused by multiplexing; and a photodetector detecting an intensity of the interference light output from the coupling unit, wherein the photo detector comprises: a silicon substrate comprised of a semiconductor of a first conductivity type, having a first principal surface and a second principal surface opposed to each other, and having a semiconductor region of a second conductivity type formed on the first principal surface side; and a transfer electrode part provided on the first principal surface of the silicon substrate and transferring a generated charge, a silicon substrate comprised of a semiconductor of a first conductivity type, having a first principal surface and a second principal surface opposed to each other, and having a semiconductor region of a second conductivity type formed on the first principal surface side; and a transfer electrode part provided on the first principal surface of the silicon substrate and transferring a generated charge, wherein in the silicon substrate, an accumulation layer of the first conductivity type having a higher impurity concentration than the silicon substrate is formed on the second principal surface side and an irregular asperity is formed in a region opposed to at least the semiconductor region of the second conductivity type, in the second principal surface, and wherein the region in which the irregular asperity is formed in the second principal surface of the silicon substrate is optically exposed.