PURPOSE: To perform primary covering work safely and economically by a method in which a side plate with a press frame is pressed on the excavated face, the press frame is twisted to the excavated face or the opposite side of it in the excavating direction of tunnel as axis, and concrete is packed into the aperture.

CONSTITUTION: A side plate 4 is provided to the side end 12 to be the facing side of tunnel at the time of using a press frame 2, and a side plate aid 13 is provided on the facing side from the side plate 4. A reinforcing plate 17 is fixed to the back face 5 of the frame 2 so that the frame 2 is not deformed flexionally in the longitudinal direction but deformed tortionally to the excavated face 1 side or to the opposite side of it at the excavation direction of tunnel as axis. The frame 2 is set with a spacing 3 in the face of the excavated face 1 of tunnel and concrete is packed into the space 3. The primary covering work of concrete layer can have nearly uniform thickness even when the excavated face 1 to be touched by the side plate 4 is extremely uneven.