An image scanning unit comprising: a light source unit (La) including a light guide which is formed into a rod-like shape extending in a main scan direction and has an end face at one end thereof for taking in light, a diffuse reflecting surface for diffusely reflecting the light taken in from the end face, and a light exit surface for emitting the light that is diffusely reflected at the diffuse reflecting surface towards an irradiation surface; a light source (41, 42) facing the end face of the light guide; and a light guide holder member holding the light guide; an image reading section (7, 8) receiving reflected light from the irradiation surface; a plurality of reflecting members (10a, 10b, 10c, 10d, 10e, 10f) forming a reading light path guiding the reflected light from the irradiation surface to the image reading section (7, 8); and a frame housing the light source unit (La), the image reading section (7, 8) and the plurality of reflecting members (10a, 10b, 10c, 10d, 10e, 10f), wherein the frame has a space inside thereof on a side facing the irradiation surface, the space being divided into two including a first space for housing the light source unit (La) and a second space adjacent to the first space for housing the plurality of reflecting members (10a, 10b, 10c, 10d, 10e), characterized in that the plurality of reflecting members (10a, 10b, 10c, 10d, 10e) include a first reflecting member which first receives the reflected light from the irradiation surface and is disposed on a side opposite to the irradiation surface with respect to the light source unit (La), a second reflecting member which receives the reflected light from the first reflecting member, and other reflecting member or members (10c, 10d, 10e) than the first and second reflecting members (10a, 10b), which is or are disposed on a side of the irradiation surface with respect to the reading light path from the first reflecting member to the second reflecting member, and, a light-shielding member (13a, 13b, 13c, 13d, 13e, 13f) to prevent the light from the first reflecting member that has strayed from the reading light path from entering the other reflecting member or members (10c, 10d, 10e) is provided by the light guide holder member or a holder retaining member that retains the light guide holder member. a light source unit (La) including a light guide which is formed into a rod-like shape extending in a main scan direction and has an end face at one end thereof for taking in light, a diffuse reflecting surface for diffusely reflecting the light taken in from the end face, and a light exit surface for emitting the light that is diffusely reflected at the diffuse reflecting surface towards an irradiation surface; a light source (41, 42) facing the end face of the light guide; and a light guide holder member holding the light guide; an image reading section (7, 8) receiving reflected light from the irradiation surface; a plurality of reflecting members (10a, 10b, 10c, 10d, 10e, 10f) forming a reading light path guiding the reflected light from the irradiation surface to the image reading section (7, 8); and a frame housing the light source unit (La), the image reading section (7, 8) and the plurality of reflecting members (10a, 10b, 10c, 10d, 10e, 10f), wherein the frame has a space inside thereof on a side facing the irradiation surface, the space being divided into two including a first space for housing the light source unit (La) and a second space adjacent to the first space for housing the plurality of reflecting members (10a, 10b, 10c, 10d, 10e), characterized in that the plurality of reflecting members (10a, 10b, 10c, 10d, 10e) include a first reflecting member which first receives the reflected light from the irradiation surface and is disposed on a side opposite to the irradiation surface with respect to the light source unit (La), a second reflecting member which receives the reflected light from the first reflecting member, and other reflecting member or members (10c, 10d, 10e) than the first and second reflecting members (10a, 10b), which is or are disposed on a side of the irradiation surface with respect to the reading light path from the first reflecting member to the second reflecting member, and, a light-shielding member (13a, 13b, 13c, 13d, 13e, 13f) to prevent the light from the first reflecting member that has strayed from the reading light path from entering the other reflecting member or members (10c, 10d, 10e) is provided by the light guide holder member or a holder retaining member that retains the light guide holder member.