An image reading device (1) includes a board (24) including a plurality of imaging elements (23) arranged along a scanning direction, and a housing (13) including (i) a plurality of optical components that are arranged along the scanning direction and (ii) a plurality of housing components (13a, 13b) that are arranged along the scanning direction. Each of the plurality of optical components focuses light reflected by a reading target onto a corresponding imaging element (23), and each of the plurality of housing components holds at least one optical component. The plurality of housing components (13a, 13b) are arranged to have a clearance therebetween and each of the plurality of housing components (13a, 13b) is fixed to the board (24) at a position to transmit light through the optical components to focus onto the corresponding imaging element (23).