A flexible substrate position control device (100) in a processing device, which transports a band-shaped flexible substrate (1) in a horizontal direction and in a vertical orientation and carries out processing of the substrate by processing units installed in a transport path of the substrate, is provided with: a pair of clamping rollers (131,132) that clamp an upper edge of the substrate; a support mechanism (140) that rotatably supports the pair of clamping rollers while allowing these rollers to mutually contact and separate from each other; urging means (150) for applying pressing force to the pair of clamping rollers through the support mechanism; and adjusting means (160) for adjusting the pressing force applied by the urging means. The pair of clamping rollers has an inclination, in which the direction of pressing relative to the clamping surface of the substrate is towards the edge of the substrate in the width direction, and is supported such that the rotating direction at the clamping surface is the same direction as the transport direction of the substrate. This flexible substrate position control device is able to inhibit the occurrence of sagging and wrinkling of a band-shaped flexible substrate, and together with realizing high-quality processing, is able to deal with transporting a flexible substrate in an opposite direction.