To provide a guide pin easily installed on a foundation, low in cost and suppressing the lateral dislocation of a building unit or the like and provide a guide pin fixing method and a building unit installation method using the guide pin.

This guide pin 1 erectly provided at a foundation top end 5 comprises a cylindrical fixed part 2 fixed to the foundation top end 5, and a guide pin body 3 with a taper 31. An external thread 21 is threaded on the outer periphery of the fixed part 2, and the guide pin body 3 is provided with an internal thread 32 thread-fastened to the external thread 21. In this guide pin fixing method, the fixed part 2 is fixed to the foundation top end 5 by a fastener such as a concrete nail or a concrete machine screw, and the external thread 21 of the fixed part 2 is screwed into the internal thread 32 of the guide pin body 3 to fix the guide pin body 3 in the state of covering the fixed part 2.