By irradiating a sample with an unfocused ion beam, processing accuracy of an ion milling device for processing a sample or reproducibility accuracy of a shape of a processed surface is improved. Therefore, the ion milling device includes a sample chamber, an ion source position adjustment mechanism provided at the sample chamber, an ion source attached to the sample chamber via the ion source position adjustment mechanism and configured to emit an ion beam, and a sample stage configured to rotate around a rotation center. When a direction in which the rotation center extends when an ion beam center of the ion beam matches the rotation center is set as a Z direction, and a plane perpendicular to the Z direction is set as an XY plane, the ion source position adjustment mechanism is capable of adjusting a position of the ion source on the XY plane and a position of the ion source in the Z direction.