A new instrument that can measure oxygen demand at sea bottom has been developed; the continuous measurement is available by repeating open and close system. The results of the field measurement at the inner part of Hiroshima Bay, whose sediment is organically enriched or polluted, showed that the average oxygen demand was about the same as another reported values and ranging from 1.31 to 1.61g/m²/d. And the data during the low atmospheric pressure passing implied that marine environment disturbance might influence the oxygen demand strongly through curling up sediment.