A speech recognition (SR) dictionary switching unit selects a SR dictionary including commands that are for controlling target devices and selectable in current operating states detected by a device-state detecting unit. When a SR engine recognizes an uttered command of a user, it collates the speech with the commands included in the selected SR dictionary. If the command is not selectable in the current operating states of the target devices and is one of a reciprocal pair of commands working oppositely to each other, the other of the reciprocal pair is substituted for the command. This results in decreasing unreasonable and unpleasant feeling of the user in voice manipulation.