The present invention discloses a coin operated device, whereby the articles inside the locker can still be taken out with the spare key of the locker provider without damaging the coin operated device when the key is lost. This method comprises a step of circulating part of a discharged gas from an absorption step of acrylic acid to the reactor and discarding the remainder to the out side of system while the gas is cooled before circulation to the reactor. An embossed portion diffusing the light emitted from the light-emitting diode is formed on the front panel. The load-related engine speed fluctuation is indicative of an engine load. Passive control involves providing cost incentives or disincentives during low or peak periods of traffic intensity.