To provide a self-standing cofferdam structure and a self-standing cofferdam method excelling in workability and economical efficiency by allowing a cylindrical temporary body to self-stand by timbering members rising along the internal wall surface of the cylindrical temporary body while totally dispensing with struts.

A cylindrical temporary body 1 is provided on a foundation of an underwater bridge pier 10 to surround the underwater bridge pier 10, and a plurality of timbering members 2 arranged inside the cylindrical temporary body and rising along the internal wall surface of the cylindrical temporary body to prevent deformation of the cylindrical temporary body are installed with bolts inside a working space 12. Each timbering member includes a post member 21, a horizontal member 22 and/or a diagonal member 23. The top end of the post member is set to a height not lower than the water level H, and a partition member 3 is provided in ring shape to face the internal wall surface of the lower end of the cylindrical temporary body. Cut-off concrete 4 is placed in a recessed ditch part formed between the cylindrical temporary body 1 and the partition member 3.