A radiation therapy apparatus on which quality management is performable, the radiation therapy apparatus comprising: a body unit; a gantry coupled to one side of the body unit and formed to be rotatable in at least one direction with regard to the body unit; a radiation irradiating head formed at one side of the gantry to irradiate a radiation; and a level control module formed at one side of the radiation irradiating head to measure a rotation angle of the gantry or the radiation irradiating head, compare the measured rotation angle with a rotation angle indicated by an angle indicator of the radiation therapy apparatus, and correct an error of the angle indicator, wherein the level control module comprises: one or more electronic level meters for measuring a rotation angle of the gantry or the radiation irradiating head; and a control unit for comparing the rotation angle of the gantry or the radiation irradiating head measured by the electronic level meter with a rotation angle indicated by an angle indicator of the radiation therapy apparatus and correcting an error of the angle indicator, the radiation therapy apparatus further comprising a control module configured to calculate a rotation speed of the gantry or the radiation irradiating head and angle information of the gantry or the radiation irradiating head at a particular time by using measurement time information and the rotation angle of the gantry or the radiation irradiating head measured by the level control module, and to compare the calculated rotation speed and an angle of the gantry or the radiation irradiating head at a particular time with a rotation speed of the gantry or the radiation irradiating head predetermined at the time of radiation therapy planning and an angle of the gantry or the radiation irradiating head at a particular time. a body unit; a gantry coupled to one side of the body unit and formed to be rotatable in at least one direction with regard to the body unit; a radiation irradiating head formed at one side of the gantry to irradiate a radiation; and a level control module formed at one side of the radiation irradiating head to measure a rotation angle of the gantry or the radiation irradiating head, compare the measured rotation angle with a rotation angle indicated by an angle indicator of the radiation therapy apparatus, and correct an error of the angle indicator, wherein the level control module comprises: one or more electronic level meters for measuring a rotation angle of the gantry or the radiation irradiating head; and a control unit for comparing the rotation angle of the gantry or the radiation irradiating head measured by the electronic level meter with a rotation angle indicated by an angle indicator of the radiation therapy apparatus and correcting an error of the angle indicator, the radiation therapy apparatus further comprising a control module configured to calculate a rotation speed of the gantry or the radiation irradiating head and angle information of the gantry or the radiation irradiating head at a particular time by using measurement time information and the rotation angle of the gantry or the radiation irradiating head measured by the level control module, and to compare the calculated rotation speed and an angle of the gantry or the radiation irradiating head at a particular time with a rotation speed of the gantry or the radiation irradiating head predetermined at the time of radiation therapy planning and an angle of the gantry or the radiation irradiating head at a particular time. one or more electronic level meters for measuring a rotation angle of the gantry or the radiation irradiating head; and a control unit for comparing the rotation angle of the gantry or the radiation irradiating head measured by the electronic level meter with a rotation angle indicated by an angle indicator of the radiation therapy apparatus and correcting an error of the angle indicator, the radiation therapy apparatus further comprising a control module configured to calculate a rotation speed of the gantry or the radiation irradiating head and angle information of the gantry or the radiation irradiating head at a particular time by using measurement time information and the rotation angle of the gantry or the radiation irradiating head measured by the level control module, and to compare the calculated rotation speed and an angle of the gantry or the radiation irradiating head at a particular time with a rotation speed of the gantry or the radiation irradiating head predetermined at the time of radiation therapy planning and an angle of the gantry or the radiation irradiating head at a particular time.