In a factory with a multi-stage production system, push-type scheduling methods can hardly improve the production rate without increasing the stocks of intermediates. For products whose specifications are known before their orders, a pull-type scheduling method named Kanban system has been developed, and has succeeded to improve the production rate without increasing the stocks of intermediates. The Kanban system, however, is not applicable to custom-made products whose specifications are not known before their orders. In this paper, a "Virtual Kanban (VK) system" is presented as a pull-type scheduling method which is applicable to custom-made products, and its usefulness is demonstrated by simulation of an application specific integrated circuit manufacturing facility.