To provide a lower aldehyde removing material efficiently removing lower aldehydes contained in a gas to be treated.

The treatment liquid 200 is a solution to remove acetaldehyde out of the gas to be treated by coming into contact with the gas containing acetaldehyde. The treatment liquid 200 contains a solvent and L-threonine dissolved in the solvent, which is controlled so that a pH of the solution could not be lower than 12 before the contact with the gas to be treated.