In an installation device of a reactor repair device and a method, an installation pole (111) connected with an upper portion of a water jet peening device (101), a lifting device (112) that can suspend and support an upper portion of the installation pole (111) and can lift the installation pole (111) from a work floor (121), a moving device (113) that can move the lifting device (112) in two directions intersecting in a horizontal direction, and a position adjustment device (114) that can move the installation pole (111) in the horizontal direction in a state where the installation pole (111) is supported by the lifting device (112).