A belt traveling unit, comprising: a plurality of rollers (18, 19a, 19b, 19c, 19d, 20); an endless belt configured to be spanned between the plurality of rollers, the plurality of rollers (18, 19a, 19b, 19c, 19d, 20) including: a drive roller; and a correction roller, a driving unit configured to rotate the drive roller to drive the belt; a correction unit configured to adjust a tilt angle of the correction roller to correct drifting of the belt in the width direction thereof; a contact member configured to be rotatable along with traveling of the belt in the width direction thereof; a position detector configured to detect a position of the contact member to detect a position of the belt in the width direction thereof by detecting a change in a distance between the position detector and the contact member; characterized in that the belt travelling unit further comprises: a supporting member configured to support the position detector; and a regulating member disposed on the horizontal side of the contact member facing a bottom surface of the supporting member, wherein when the contact member moves in conjunction with a travelling motion of the belt in the width direction, the regulating member comes into contact with the supporting member which is configured to support the position detector, in order to regulate the distance between the horizontal side of the contact member and the position detector. a plurality of rollers (18, 19a, 19b, 19c, 19d, 20); an endless belt configured to be spanned between the plurality of rollers, the plurality of rollers (18, 19a, 19b, 19c, 19d, 20) including: a drive roller; and a correction roller, a drive roller; and a correction roller, a driving unit configured to rotate the drive roller to drive the belt; a correction unit configured to adjust a tilt angle of the correction roller to correct drifting of the belt in the width direction thereof; a contact member configured to be rotatable along with traveling of the belt in the width direction thereof; a position detector configured to detect a position of the contact member to detect a position of the belt in the width direction thereof by detecting a change in a distance between the position detector and the contact member; characterized in that the belt travelling unit further comprises: a supporting member configured to support the position detector; and a regulating member disposed on the horizontal side of the contact member facing a bottom surface of the supporting member, wherein when the contact member moves in conjunction with a travelling motion of the belt in the width direction, the regulating member comes into contact with the supporting member which is configured to support the position detector, in order to regulate the distance between the horizontal side of the contact member and the position detector. a supporting member configured to support the position detector; and a regulating member disposed on the horizontal side of the contact member facing a bottom surface of the supporting member, wherein when the contact member moves in conjunction with a travelling motion of the belt in the width direction, the regulating member comes into contact with the supporting member which is configured to support the position detector, in order to regulate the distance between the horizontal side of the contact member and the position detector.