NOVELTY - The processing apparatus which surface-treats the flexible substrate (1) conveyed along a longitudinal direction has an unwinding chamber (3), where the flexible substrate is unwound from a roll (6) and conveyed. A heating mechanism containing a roll core heater (11) performs preheating and degassing process to the core of the flexible substrate unwinding roll. A non-contact type heating mechanism (12) positioned on the outer side of the unwinding roll heats the flexible substrate as it is unwound.    USE - Apparatus for processing such as preheating, degassing, and material modification of surface of flexible substrate such as flexible substrate of photoelectric conversion element used for e.g. solar cell.    ADVANTAGE - The flexible substrate can be reliably preheated prior to the film forming process by the roll core heater, without requiring a large sized heating chamber. Further the impurity components such as water molecule adsorbed on the flexible substrate can be removed reliably. Reduction in size, cost and effective usage of installation space are achieved by using the roll core heater for preheating and degassing process the core of flexible substrate unwinding roll. The flexible substrate can be surface treated to high quality standard in a short time. The outer side of the unwinding roll can be effectively preheated and degassed by the non-contact type heating mechanism positioned on the outer side of the unwinding roll. The temperature of the flexible substrate and the core temperature of the unwinding roll can be controlled by a high precision. Process conditions can be controlled by high precision by feedback control, and necessary and sufficient heat processing can be performed to the flexible substrate.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional schematic view of the flexible substrate processing apparatus.    Flexible substrate (1)    Unwinding chamber (3)    Roll (6)    Roll core heater (11)    Non-contact-type heating mechanism (12)