Disclosed is a novel means that enables mass production of highly safe fibrinogen at low cost. The transgenic silkworm of the present invention expresses the fibrinogen subunit Aα, Bβ and γ chains in the silk gland cells and produces fibrinogen having coagulation activity in the cocoon filament. Preferably, the transgenic silkworm expresses the subunits in the middle silk gland cells and produces fibrinogen in the sericin layer of the cocoon filament. By recovering fibrinogen from the cocoon of the transgenic silkworm of the present invention, highly safe fibrinogen can be mass-produced at low cost.