Joint structure for steel pipe pile, steel pipe pile foundation, and method of building steel pipe pile foundation

A joint structure for a steel pipe pile, comprising: a steel pipe pile's first main pipe; a steel pipe pile's second main pipe which is adjacent to the steel pipe pile's first main pipe; a male joint which is provided with a pair of male legs mounted to the steel pipe pile's first main pipe and also with a pair of male arms extending from the male legs so as to separate from each other, and which has protrusions and depressions formed on the surface thereof; a female joint which is provided with a pair of female legs mounted to the steel pipe pile's second main pipe and also with a pair of female arms extending from the female legs so as approach each other, and which is engaged with the male joint; and a plate-like member which is provided to the steel pipe pile's second main pipe at a position between the pair of female legs, and which has protrusions and depressions formed on the surface thereof.