A drive device for an in-core neutron instrumentation system includes a safety circuit between a power supply and a drive motor. The safety circuit is provided inside the cover member, and switches between a conductive state in which power can be supplied to the drive motor and a cut-off state in which power cannot be supplied thereto depending on a mounted state of the cover member. The safety circuit is controlled to be in the conductive state in response to a state in which the cover member is mounted on the base member, and is controlled to be in the cut-off state in response to a state in which the cover member is not mounted on the base member.