The purpose of the present invention is to provide a plant information sharing system capable of hierarchizing information retained by a plant monitoring-control system into a plurality of levels according to content and carrying out information management and data transmission management. Provided is a plant information sharing system (1), wherein a monitoring-control system (10): transmits in real-time to a maintenance system (50) the monitoring-control information wherefor transmission is pre-approved, from among monitoring-control information stored in a first-level plant database (13); transmits, according to the outcome of an assessment on whether to approve the transmission, a requested setting value information from among monitoring-control setting values stored in a second-level plant database (14); and transmits, according to the outcome of the assessment on whether to approve the transmission, the plant operation records matching the requested content and interval, from among past plant operation r
