PURPOSE: To uniformize a wall thickness distribution and a fiber distribution even in the production of a thin-wall fibrous composite sheet.

CONSTITUTION: A reinforcing fiber strand F1 of a large number of continuous monofilaments is passed through a powdered thermoplastic resin while coming into contact with a vibration application rotating body 6 disposed in a powdered thermoplastic resin fluidizer 1. In this manner, a vibration of a fixed period is applied to the reinforcing fiber strand F1 to accelerate the opening of the reinforcing fiber strand F1; the powdered thermoplastic resin F2 adheres to the respective monofilaments to be caught between the monofilaments. The thermoplastic resin of the opened resin-adhering fiber F2 is heated and melted into a sheet form. In this manner, a fibrous composite sheet S is obtained.