To provide a belt device capable of reducing a size and a manufacturing cost by enhancing driving efficiency.

An electric motor 10 of the belt device 1 is provided with first and second magnetic pole rows 11 and first and second armature rows 12 provided on a fixed member CA, and soft magnetic body rows 13, 14 provided on a belt 3, respectively having a plurality of first and second magnetic poles 11a, first and second armatures 12a, and soft magnetic bodies 13a, 14a. When the polarity of the first armature magnetic pole of the first armature 12a is different from the polarity of the first magnetic pole 11a opposite thereto, the polarity of the second armature magnetic pole of the second armature 12a is the same as the polarity of the opposing second magnetic pole 11a. Furthermore, when the soft magnetic body 13a between the first magnetic pole row 11 and the first armature magnetic pole 12 is located between the first magnetic pole 11a and the first armature magnetic pole, the soft magnetic body 14a between the second magnetic pole row 11 and the second armature row 12 is located between two sets of the second armature magnetic poles and the second magnetic poles 11a adjacent to each other in the longitudinal direction of the belt 3.