To manufacture a prepreg almost free from voids using a soaking process by first feeding a fiber base material onto an introduction roll in an impregnation tank and impregnating the fiber base material with a resin varnish in such a manner that the fiber base material is fed onto an impregnation roll so as to make the face coming into contact with the introduction roll come into contact with the opposite side face to the former.

An outward pressure from an introduction roll 3, that is, a pressure to be applied to the opposite side face (b) to the face (a) coming into contact with the introduction roll 3 from the face (a), works following the feeding of a fiber base material 1 onto the introduction roll 3. Next the pressure makes a resin varnish flow from the face (a) to the face (b) and in turn, air bubbles are pushed out of the face (b) side. After that, the fiber base material 1 is fed onto the impregnation roll 7 in such a manner that the opposite side face (b) to the face (a) coming into contact with the introduction roll 3 comes into contact with the impregnation roll 7. Consequently the pressure to be applied to the opposite side face (a) from the face (b) coming into contact with the impregnation roll 7 works to force air bubbles out of the face (a) side. Thus the air bubbles are removed from the resin varnish with which the resin base material 1 is impregnated.