In a substrate processing device, a technique that achieves OR transfer satisfying a specified condition is provided. The substrate processing device includes an identifying unit configured to refer to usage states of a plurality of process modules at process time slots to identify one or more process modules that can execute processes of substrates included in a control job to be processed among process modules that can be used at the process time slots, a calculating unit configured to assign the processes of the substrates to respective process time slots of the one or more process modules identified by the identifying unit to calculate a time duration from a start to an end of the processes of the substrates, and a determining unit configured to determine start timing of starting the processes of the substrates so that the time duration calculated by the calculating unit satisfies a specified condition.