To provide a continuous bias-reinforced fiber sheet hardly changing an oriented angle of the reinforcing fiber even when a tensile force is added in the longitudinal direction of the bias-reinforced fiber sheet or the width direction of the bias-reinforced fiber sheet, sufficiently satisfying in quality side, and capable of providing a long fiber-reinforced plastic structural material having extremely improved torsional rigidity.

The bias-reinforced fiber sheet is obtained by arranging a resin-permeable supporter sheet 2 at least on one surface of at least one layer of a reinforcing fiber layer 3 arranged along the longitudinal direction of the bias-reinforced fiber sheet 1 formed by arranging the reinforcing fiber so that the arranged angle (α) of the reinforcing fiber may be a prescribed angle to the axis line in the longitudinal direction of the bias reinforced fiber sheet 1, and integrating the reinforcing fiber layer 3 with the resin-permeable supporter sheet 2 by stitching (S) along the longitudinal direction of the bias reinforced fiber sheet.