Following the insertion of a trial key or a license key into a port, authentication thereof is executed (S4, S22); if the trial key authentication is successful, a trial time limit is obtained by adding a trial permission period to a current time and is stored into a nonvolatile memory (S25); if the current time exceeds the trial time limit (S12, S13), or the license key authentication is successful, the trial state information is changed to indicate “trailed” (S4); if the license key authentication is successful (S14), or the trial key authentication is successful (S15) and the trial state information does not indicate “trialed” (S16), an optional routine is executed following an instruction from a control panel. In that routine, if the trial state information does not indicate “trialed”, the trial time limit is displayed on a control panel.