Abstract: In order to more reliably prevent a runner from being disengaged from a rail during using of a fixation band, a subject fixing device of the present invention includes a runner includes a runner main body that is accommodated inside a rail, and a band connection portion that protrudes out of the rail and is connected to the fixation band, and a rail includes a rail main body that slidably holds the runner main body, and first and second attachment portions that protrude outwards from the rail main body, and are disposed with an end of the fixation base interposed therebetween so as to be attached to the fixation base, and in which the rail main body is provided with a slit which allows the band connection portion to pass therethrough, and prevents the runner main body from passing therethrough, along a longitudinal direction of the rail main body.