An image reading device includes a casing, an image reading unit, a mounting board, and an antenna. The casing has a side wall positioned at one end thereof in a first direction. The image reading unit is accommodated in the casing and configured to read an image of an original document by scanning in the first direction. The mounting board is accommodated in the casing and mounts an electronic component that is used when the image reading unit reads the image, the mounting board extending in the first direction. The antenna is accommodated in the casing and configured to receive or transmit a radio signal. The antenna is disposed along and adjacent the side wall.