A belt conveying device includes: at least three rollers, about which an endless belt to convey an object, is entrained, including an oscillation roller having a rotation shaft, whose one end is fixed and another end is oscillatably supported; a belt detection sensor provided adjacent to a side edge of the belt, which detects presence of the belt; and a belt skew controller which controls the oscillator to oscillate the oscillation roller according to a preset control value in a predetermined range to correct skew. The oscillator moves a rotation center of a movable edge of the oscillation roller along a tangential line of an ellipse having elliptical focuses corresponding to rotation centers of rotation shafts of the two rollers, other than the oscillation roller, positioned respectively in upstream and downstream of and adjacent to the oscillation roller in a belt conveyance direction.