A beamline device includes a deflection device deflecting an ion beam in a first direction perpendicular to a beam traveling direction by applying at least one of an electric field and a magnetic field to the ion beam. A slit is disposed such that the first direction coincides with a slit width direction. A beam current measurement device is configured to be capable of measuring a beam current at a plurality of measurement positions to be different positions in the first direction. A control device calculates angle information in the first direction on the ion beam by acquiring a plurality of beam current values measured at the plurality of measurement positions to be the different positions in the first direction by the beam current measurement device while changing a deflection amount of the ion beam in the first direction with the deflection device.