To provide a rectangular pipe body that can form a recess for interference prevention, while evading a local decrease in strength caused by forming the recess for interference prevention.

The rectangular pipe body 1 is formed from a rectangular metal sheet 6. Abutting walls 5a, 5b forming an abutment 5e are made closely contact each other driven by internal stress in a bottom wall 2. And also the abutting walls 5a, 5b form a bent configuration (recess 53 for interference prevention) having a different height against the bottom wall 2.