To enable the long-term repetitive use of a crucible for producing a bismuth substd. rare earth iron garnet single crystal by providing the inner side of a platinum crucible with a corrosion preventive zone made of platinum separable from this platinum crucible to prevent the flow of melt from extending to a crucible body.

The inner side of the platinum crucible is provided with the corrosion preventive zone made of the platinum separable from the platinum crucible. The corrosion preventive zone made of the platinum which is smaller by about 0.3 to 20 mm in the outside diameter than the inside diameter of the platinum crucible and is about ≥25 mm in the width is preferable. This zone is preferably disposed within a range of an upper part 5 mm to a lower part 20 mm than the melt surface. The role of the corrosion preventive zone is to prevent the influence of the flow of the melt by rotation of a substrate at the time of stirring or crystal growth from being exerted on the crucible body. The progression of corrosion when the production of the single crystal is repeated is around the melt surface of the corrosion preventive zone and the corrosion of the crucible body does not occur. The corrosion preventive zone is replaced before the corrosion preventive zone is bored with a hole upon progression of the corrosion.