To provide a spiral anchor and its installation method capable of increasing working efficiency while reducing the production cost of a steel pipe by facilitating the positioning thereof in installation and completely reinforcing a soft ground by steel pipe piles improved in a facilitated and secure operating state.

In this spiral anchor pile 6 formed of a hollow pile body having a closed lower end part, a small diameter tip part 4 with an spiral blade 5 is fitted to the lower end part of the pile body 7, a spiral blade 3 having the same pitch as that of the spiral blade 5 at the tip part 4 is fitted to at least the lower end peripheral surface of the pile body, and a plurality of anchor pins 8 extrudable to the peripheral surface of the pile body are installed at specified intervals.