Provided is an image-reading device (25) for reading an image by moving a recording medium (M) and a reading range (R) relative to each other, the recording medium (M) having the image recorded thereon and the reading range (R) being a range in which a part of the image is read, the device including: a light source (253); a light-blocking part (251) which blocks light that is emitted from the light source (253) and goes toward the recording medium (M); and a reading means (255) which reads the image recorded on the recording medium (M) by detecting light that passes through a slit (251a) provided in the light-blocking part (251) from among reflected light of light that is emitted from the light source (253), passes through the slit (251a) and enters the reading range (R) in the recording medium (M).