A technology that prevents leak of patient data, which is personal information, stored in a storage medium without requiring labor is disclosed. According to the technology, when a command for bulk-deleting pieces of data stored in memories 4 to 7 is entered using an operating unit 1 (Step 1), the pieces of data stored in the memories are bulk-deleted (Step S2). When a hospital name, a language to be used, a time zone, preset data, or user-customized data registered in advance is changed, a device is judged to have been resold. The pieces of data stored in the memories are bulk-deleted (Step 2).