A decontamination process device includes a chamber that contains a decontamination target, a heating device that generates decontamination vapor, an air sending part that sends the decontamination vapor into the chamber, a ventilation system that ventilates the chamber, a controller that controls operations of the decontamination process device. The controller performs a supply process that supplies the decontamination vapor into the chamber and an elimination process that eliminates a decontamination component after the supply process. The ventilation system adjusts an ventilation amount and the controller is set to repeat the supply processes at multiple times, and to perform a dry process between the repeated supply processes and to maintain the chamber at a positive pressure during the dry process.