A hearing aid adjustment device (1) has a comparator (22a) and a setting section (22b). The comparator (22a) compares a user evaluation given by a user (T) of a hearing aid (5) in response to sound obtained by hearing aid processing based on fitting theories and hearing level data for the user (T), with a reference evaluation that has been acquired ahead of time and corresponds to each of customers (A to C) and is given by the customers (A to C) in response to sound obtained by hearing aid processing based on fitting theories and hearing level data for the customers (A to C). The setting section (22b) sets the value of a user parameter designating hearing aid processing to be given to a user (T), to a value that is the same as the value of a reference parameter that has been acquired ahead of time and that designates hearing aid processing suited to a customer (A) who gave a reference evaluation similar to the user evaluation, out of the customers (A to C).