A paper transport device includes a transport section that transports paper on a first transport path, and reverses a transport direction to transport the paper onto a second transport path, and a detecting section that detects that the paper has arrived at the reversal position, wherein the detecting section includes a first member that is arranged on the first transport path, and changes posture thereof among a first posture, a second posture, and a third posture, a second member that changes posture thereof between a fourth posture and a fifth posture, a detector that detects whether the second member is in the fourth posture or in the fifth posture, and a joint member that couples the first member and the second member together, allows the second member to be in the fourth posture, rotates the second member to the fifth posture, and keeps the second member in the fourth posture.