A printing apparatus comprises a print head moving module comprising a mounting plate, a first wheel, a second wheel, an endless belt, a retaining member of the mounting plate to clamp with the second wheel; an adjusting device comprising a positioning member of the mounting plate, a driving member of the positioning member comprising an indicating block, a moveable member of the positioning member abutting the retaining member, the moveable member comprises a receiving portion having graduations; the indicating block is through the positioning member in the receiving portion; a resilient member in the receiving portion between the driving and the moveable members; wherein the driving member drives the moveable and the retaining members from a first to a second position, in the first position, the indicating block is away from a predetermined graduation; in the second position, resilient member deformed, the indicating block is at the predetermined graduation.