There is disclosed an audio recorder that automatically determines, when preset microphones are configured to be detachable and different microphones are attached to the same jacks, whether or not the different microphones are in-house microphones, and automatically determines which of the X-Y technique or the A-B technique is used as the attachment technique. Holders in the audio recorder include a switch structure in which, in cases where the different microphones are attached in place of the preset microphones, a contact is turned on only when the different microphones are in-house microphones. Further, a main body unit includes a processor that, when the contact in the switch structure is turned on, automatically determines which of the X-Y technique or the A-B technique is used based on a voltage value of a certain terminal in a plug of the different microphones.