A sound volume adjuster includes: a storage which stores a first value of a volume setting value and an allowable maximum change amount; a receiver which receives a change request indicating a second value of the volume setting value; a determiner which, when a change amount of the volume setting value between the first value and the second value exceeds the allowable maximum change amount, determines that the change request is an excessive request; and an adjuster which, when the determiner determines that the change request is the excessive request: changes the first value stored in the storage by a change amount which is equal to or smaller than the allowable maximum change amount to set a third value of the volume setting value; and adjusts a sound volume by the third value.