Provided is an image scanning unit which makes it possible to improve scanning accuracy while also making the overall body thinner by appropriately positioning a plurality of reflection members within an effective space in a carriage frame without wasting space. An image scanning unit, wherein a frame is divided into at least two spaces facing an irradiation surface, a first accommodation unit for accommodating a light source unit is formed in one of the spaces, a second accommodation unit for accommodating at least one reflection member is formed in the other adjacent space, a first reflection member for initially receiving light reflected from the irradiation surface is positioned at the side opposite the irradiation surface with the first accommodation unit positioned therebetween, and a light-shielding member is provided between the first reflection member and the reflection member positioned in the other space and prevents light that has strayed from a scanning light path from the first reflection member from being incident on the reflection member in the other space.