To decrease a sensing distance of an original sensor with respect to an original by allowing the reader to have a 1st original sensing means that is placed on a mobile object and senses presence of an original on an original platen and a 2nd sensing means that is placed fixedly at a position not disturbing movement of the mobile object and senses the presence of the original on the original platen.

The reader is provided with an optical carriage (mobile object) 10 that contains a reflection mirror 7 reading an image of an original 1 through scanning, a image forming lens 8, and an image sensor 9 or the like movable along the original 1. The original sensors (1st original sensing means) 20a, 20b, 20c, 20d are placed sequentially at a right angle in a mobile direction of the optical carriage 10 so as to be overlapped with the original 1 of a prescribed size. Furthermore, an original sensor (2nd original sensing means) 20e is placed to overlap only an A3 size original 1a and a B4 size original 1d at a position apart from the original sensors 20a-20d.