In the light-receiving element array device according to the present invention, a light-receiving section can be arranged at a position close to an input optical fiber so that the light-receiving element array device can be used as an optical demultiplexer based on the Littrow arrangement. Further the present invention enables suppression of coma aberration and minimization of an optical demultiplexer by shortening a length of the optical system. To achieve the above-described object, a rectangular chip having a light-receiving section with a number of light-receiving elements arrayed in row thereon is sealed in a rectangular package having external leads and the bonding pads on the chip and the bonding terminals of the packages are connected with a bonding wire or the like. This light-receiving element array device has any of the following constructions: (1) in which no bonding pad is provided along one longer edge of the chip in an area around a light-receiving section of the chip, (2) in which no bonding terminal is provided along one longer edge of the package, or (3) in which no external lead is provided along one longer edge of the package, or a combination of the constructions, and the chip is accommodated in the package at a position displaced to one side of the package.