To obtain an antimicrobial and antifungal agent composition capable of sustaining antimicrobial and antifungal effects for a long period by formulating aldehydes such as cinnamic aldehyde or benzaldehyde with a specific amount of a specified crystallization inhibitor.

This antimicrobial and antifungal agent composition is obtained by including 0.001-10wt.% one or more crystallization inhibitors selected from dibutylhydroxytoluene, butylhydroxyanisole, propyl gallate, α-tocopherol, etc., in one or more aldehydes selected from cinnamic aldehyde, benzaldehyde, phenylacetaldehyde, heptylaldehyde, octyl aldehyde, decyl aldehyde, undecyl aldehyde, etc. The antimicrobial and antifungal agent is preferably used in a form for vaporization through a fragrance-permeable membrane. The fragrance-permeable membrane preferably consists essentially of polymethylpentene.