PROBLEM TO BE SOLVED: To provide a substance which more resembles a life space odor.SOLUTION: A room imitation odor composition contains acetaldehyde as a main component, and odor ingredients other than the acetaldehyde. The odor ingredients can contain trimethylamine, hydrogen sulfide, methyl mercaptan, isovaleric acid and n-valeric acid. The room imitation odor composition can contain acetaldehyde by 3±0.15 ppb, trimethylamine by 0.84±0.042 ppb, hydrogen sulfide by 0.63±0.0315 ppb, methyl mercaptan by 0.08±0.004 ppb, isovaleric acid by 1.1±0.055 ppb, and n-valeric acid by 0.09±0.0045 ppb.