1. A production schedule creation device, comprising: a production simulator that simulates a production process expressing a production state and a production constraint of the production process; a mathematical expression model holding device that holds a mathematical expression model which is created by acquiring information relating to creation of a production schedule to which attention is paid, and is a mathematical expression model expressing the production state and the production constraint of the above described production process in a mathematical expression; and an optimization calculation device that performs optimization calculation processing by using a predetermined evaluation function for the above described mathematical expression model, and calculates a production instruction for said production simulator, wherein the production instruction obtained by said optimization calculation device is supplied to said production simulator to cause it to execute simulation, an instruction to perform optimization calculation is output to said optimization calculation device from said production simulator whenever a new event occurs, and thereby said production simulator and said optimization calculation device are linked to each other to create the production schedule in the above described production process.