1. An operation simulation system for plant construction, comprising: an input apparatus for giving a command input; a heavy machinery setting apparatus for determining a type of a crane used in a construction operation based on the command input; an operation index calculation apparatus for calculating operating expenses in the operation based on the determined crane type; a foundation placement setting apparatus for determining placement of a foundation, which defines an operating range of the-determined crane; a foundation construction index calculation apparatus for calculating the expenses cost to construct a foundation based on the foundation placement; an operation period setting apparatus for determining a period during which an operation is carried out based on the command input; an operation period index calculation apparatus for calculating the operating expenses based on the determined period; an installation object setting apparatus for determining specifications of the installation object based on the command input; a temporary placement index calculation apparatus for calculating, based on the determined specifications of the installation object, the expenses cost to occupy an area in which to temporarily place the installation object before the installation object is installed; an installation milestone setting apparatus for determining a due date of the installation object based on the command input; an installation operation index calculation apparatus for calculating the installation operation expenses based on a received installation milestone; a total index calculation apparatus for calculating the total necessary expenses based on indexes calculated by the operation index calculation apparatus, foundation construction index calculation apparatus, operation period index calculation apparatus, a temporary placement index calculation apparatus and installation operation index calculation apparatus; an evaluation analysis apparatus for analyzing and evaluating calculated results; and an adjustment support apparatus for adjusting the command input based on evaluation information generated in the evaluation analysis apparatus so that the value of the command input falls in a range of set values in the specifications held by the corresponding setting apparatus.