An operation-supporting apparatus includes: an operation request input unit that inputs information relating to operation request items of plant equipment; an operating conditions setting unit that converts operation request input information to operating parameters; an operation history creation unit that creates an operation history by chronologically processing the operating parameters; a breakdown statistics database that stores an event tree of the plant equipment; an event simulator that calculates the degree of unreliability corresponding to the operating parameters, the operation request information, and the operation history information, and in compliance with the event tree; a risk-cost calculation unit that calculates risk-cost by determining the aggregate product of the degrees of unreliability and restoration costs; an operating method determination unit that determines whether operating conditions are suitable by comparing the risk-cost with profit gained by continuing operation; and an operating method specification unit that specifies specific operation conditions for the plant equipment.