An ion milling apparatus has: a sample holder including a shield member for shielding the sample except for a portion to be milled; and a sample locking member cooperating with the shield member such that the sample is sandwiched and held therebetween. The shield member has an edge portion that determines a milling position on or in the sample. The sample locking member is disposed downstream of the edge portion in the direction of irradiation by the ion beam and has a support portion cooperating with the edge portion to support the milled portion therebetween. The support portion has a first surface making contact with the sample and a second surface making a given angle to the first surface. The given angle is equal to or less than 90°.