According to one embodiment, an automatic sample preparation apparatus includes: a charged particle beam irradiation optical system configured to perform irradiation with a charged particle beam; a sample stage configured to move with the sample placed thereon; a sample piece transfer device for holding and transferring the sample piece separated and extracted from the sample; a sample piece holder-fixing bed configured to hold a sample piece holder to which the sample piece is transferred; a gas supply portion configured to irradiate gas forming a deposition film with the charged particle beam; and a computer configured to control the charged particle beam irradiation optical system, the sample piece transfer device, and the gas supply portion to transfer and stop the sample piece held by the sample piece transfer device with a gap between the sample piece holder and the sample piece, and connect the sample piece to the sample piece holder.