An image reading device according to one aspect of the invention comprises: a conveying unit configured to convey a recording medium; a first transmissive portion having a first surface that allows the recording medium to pass the first surface; a second transmissive portion having a second surface on which a recording medium is allowed to be placed; an image reading unit comprising a line sensor extending in a first direction and movable on a second path, the second path continuously extending below the first transmissive portion and the second transmissive portion; and a driver configured to move the image reading unit on the second path. A relative distance between the line sensor and the first surface changes in the second path below the first transmissive portion. The recording medium can be read at positions having the relative distances different one another.