A semiconductor chip S is formed with a plurality of photodiodes PD and comprises a plurality of output terminals T of the photodetector elements provided on the surface thereof. The circuit substrate C comprises a plurality of input terminals I to which signals from the output terminals T of the semiconductor chip S are input. The connecting means CM connects the respective output terminals T to respective input terminals I, and the interval between the input terminals I is set to a smaller dimension than the interval between the output terminals T. In this detector, since the signal reading circuit A is formed on the circuit substrate C in a region outside the region R.sub.1 where the input terminals are formed, it is possible to make the dimensions of the circuit substrate C smaller than those of the semiconductor chip S, and consequently, when a plurality of detectors D are arranged together, the respective semiconductor chips S can be positioned in mutually proximate or contacting fashion, and hence any decline in image resolution in the connecting section of the detectors can be suppressed.