A guitar amplifier and a control method of a guitar amplifier in which a setting of a performance mode can be easily changed without an interruption to a sound is provided. The guitar amplifier, which performs musical sound processing on an input musical sound and outputs it, includes a storage device which stores a plurality of information sets including a set value for each of one or two or more types of musical sound processing used in a performance mode, and a control device which changes the setting of the one or two or more types of musical sound processing to a setting according to a set value of a selected information set when information indicating ON of the performance mode, to which the selected information set from the plurality of information sets has been applied, is input.