An ion beam measuring device includes: a mask that is used for shaping an original ion beam into a measuring ion beam including a y beam part elongated in a y direction that is perpendicular to a traveling direction of the ion beam and an x beam part elongated in an x direction that is perpendicular to the traveling direction and the y direction; a detection unit that is configured to detect an x-direction position of the y beam part and a y-direction position of the x beam part; and a beam angle calculating unit that is configured to calculate an x-direction beam angle using the x-direction position and a y-direction beam angle using the y-direction position.