A device and a method for efficiently decontaminating a device used to culture cells are provided. The decontamination device for decontaminating a device is used to culture cells, manipulate microorganisms, or perform a sterility test, and comprises an ultrasonic atomizer that atomizes a peracetic acid disinfectant by using ultrasonic oscillation to discharge droplets, a diffusion fan, a temperature-humidity sensor, and a controller.