A decontamination liquid supply device including measuring means which measures a weight of a decontamination liquid stored in decontamination liquid storing means, a decontamination liquid supply passage, and delivery means which is provided midway in the decontamination liquid supply passage, and supplying the decontamination liquid of a predetermined weight to the downstream side equipment via the delivery means by measuring a weight of the decontamination liquid by the measuring means, wherein a gas supply passage for supplying a gas is connected to the decontamination liquid supply passage, an on-off valve which opens and closes the gas supply passage is provided, control means which receives a signal from the measuring means and controls opening and closing of the on-off valve is provided.
