The present invention involves mixing a chlorite aqueous solution, an activating agent which rapidly adjusts the pH of the chlorite solution, an activation inhibitor which reduces the action of the activating agent with a delay, and a metal iodide, at a ratio of not more than 0.4% by mass of metal iodide and not more than 1% by mass of activation inhibitor with respect to 1L of a 1% by mass chlorite aqueous solution, and generating, immediately and at a stable concentration, a chlorine dioxide gas from the liquid composition thus obtained.
