To simply assemble timbering for supporting temporarily a bridge girder block.

A working floor panel 4, a passage panel 4a, a slant ladder 7, a truss frame 5, etc., are plane-assembled on the ground with two bent pillars 3 made to be of a required length, so that a first bent pillar unit 6a be formed. The working floor panel 4 and the truss frame 5 are plane-assembled likewise with two bent pillars 3 so that a second bent pillar unit 6b be formed. A bent block 6 is formed by erecting the first bent pillar unit 6a and second bent pillar unit 6b oppositely and by integrating them. On the bent block 6, another bent blocks 6 are stacked up sequentially, with phases shifted by 90°, according to the same processes.