A bar code reader has two reading windows, i.e., a bottom window (5) and a side window (4). An increased number of scanning lines are used for constituting scanning patterns for scanning bar codes, and the arrangement of the optical system is contrived to decrease the whole size of the bar code reader and, particularly, to decrease the depth of the bar code reader. A source (21) of laser light, a splitter (22) for splitting the laser beam emitted from the laser light source into two, a reflection mirror (23, 24) for transmitting one beam from the splitter to a polygon mirror (25) which rotates to scan the incident laser beam, a mirror system (26) for emitting the beam reflected by the polygon mirror through the reading window (5), and a focusing member (30) for focusing the beam reflected by the bar code onto a detector (28) that detects the beam reflected by the bar code, are arranged on the same line in the bar code reader. By using a concave mirror (30), furthermore, the beam reflected by the bar code is folded back to one detector (28). The light-receiving surface of another detector (29) is faced downward to receive the beam reflected by the bar code through a Fresnel lens (32) and mirror (33), thereby to decrease the depth of the bar code reader. Furthermore, the beam passage from the reflection mirror goes through the lower surface of the polygon mirror intersecting the axis of rotation of the polygon mirror.