A belt transport device includes: a drive roller which is driven by a power source; a driven roller which is held in a rotatable manner; an endless belt which is wound on the drive roller and the driven roller; a band-like detecting section which is arranged on the endless belt in a circumferential direction of the endless belt; a sensor which detects the band-like detecting section; a displacement unit which displaces a relative positional relationship between the band-like detecting section and the sensor in a width direction of the endless belt.