A gantry positioning device for connecting a gantry and a supporter together of an imaging system includes: a linear translation positioner for translating the gantry vertically with respect to the supporter; a first rotation positioner for rotating the gantry about a first axis which passes horizontally an iso-center of the gantry with respect to the supporter; and a second rotation positioner for rotating the gantry about a second axis which passes vertically the iso-center of the gantry with respect to the supporter. The first rotation positioner includes: a tilt guide which is formed along an arc having a center on the first axis; and a tilt block which is connected to the tilt guide so as to be rotatable about the first axis.