To easily operate small-scale temporary coffering in a narrow space below a girder during aseismatic reinforcement work and the like for a bridge girder lower part when a column type structural body is immersed in the water.

In this simple coffering method around the column type structural body in reinforcement work for covering the outside face of the column type structural body (a pier 3) projected on a water bottom ground 8 with a steel plate block, a coffering steel plate 5 is assembled when divided coffering steel plate members 5a and 5b are arranged at a predetermined interval to surround the pier 3 and joints of the respective members 5a and 5b are connected together, and then, the coffering steel plate 5 is pressed down by means of a press-in jack 10 in a press-in device 4 fixed in the upper part of the pier 3 to be inserted into the water bottom ground 8. When assembly of the coffering steel plate 5 and its pressing down operation are repeated, the outside of the pier 3 is hermetically coffered by means of a plurality of coffering steel plates 5.