The present invention relates to an apparatus for adjusting a radiation field using keystone correction, and a method thereof, and more specifically, to an apparatus for adjusting a radiation field which has a light source apparatus disposed on the outside of the apparatus for adjusting a radiation field so as to match a radiation field by using keystone correction without a reflecting mirror. When radiation is irradiated, the radiation does not pass through the reflecting mirror, thereby acquiring better products than before even though it is slight, having less technological difficulty in matching a radiation field of radiation with a radiation field of visible ray in a designing and manufacturing step, and facilitating maintenance when used for a long period of time. To this end, the apparatus for adjusting a radiation field comprises: a radiation field adjustment unit for adjusting a radiation field of incident radiation a radiation emission unit for irradiating the radiation of which the radiation field is adjusted a radiation field adjustment apparatus case for performing a role of accommodating and protecting various apparatuses, and the like a light source apparatus disposed on a side lower end of the radiation field adjustment apparatus case to irradiate visible ray to be matched with a radiation irradiation range a light source radiation field adjustment apparatus disposed on a front end of the light source apparatus in order to adjust an irradiation angle and shape of a light source a light source apparatus connection unit for connecting the light source apparatus with a radiation field generation apparatus case and a light source apparatus rotation unit for rotating the light source apparatus to change a light source irradiation angle. When a radiation field is changed according to a change on the radiation field, a change on a source-to-image distance (SID) between a radiation generation apparatus and a radiation reception unit, and the like, it is poss
