Abstract: A parcel (4) installation for preparing purchase orders comprising at least an optical reading device (5) for reading bar codes. The parcels (4) are put together from products distributed in storage sectors and identified by bar codes. The device includes switches (57a, 57b) for obtaining a first, so called gun, reading mode allowing reading bar codes identifying the parcel (4) and a second, so called hand-free, reading mode for reading bar codes born by the products passing in front of the reader (53) while with the device operates in the second reading mode. Preferably, the device also includes an affixed or movable screen (52) for displaying the data read and guiding the operator.