An image sensor module includes a light source, a light guide elongated in a first direction, a reflector covering the guide, and a light receiver for linear light reflected on a reading target in a second direction perpendicular to the first direction. The guide includes an incident surface for entering light from the light source, a reflecting portion for reflecting, in a direction crossing the first direction, the light from the incident surface, and a surface for emitting light from the reflecting portion as linear light elongated in the first direction. The reflector has an opening and an inclined surface. The opening extends in the first direction to pass the light reflected by the target. The inclined surface, at an end of the opening in the first direction, has a normal which is non-parallel to the first direction and a third direction perpendicular to the first and second directions.