A hybrid method of a forward simulation and a backward simulation is proposed for enhancing the quality of a scheduling activity support. The importance of production scheduling in a manufacturing environment these days is first discussed, focusing on due-date conscious production such as make-to-order production and job shop production. Discussion then centers on simulation methods which are highly potential for the support. Further, reviewing the potentiality and limitation of a forward simulation and a backward simulation, a hybrid method of them is discussed and its effectiveness is shown not only on a simple jobshop model, but also on an actually working system.