MM-4, which distributes MIDI signals to four outputs. This is a vintage MIDI device. I have confirmed that MIDI sound sources produce sound correctly from all four outputs when a signal is input to MIDI IN. Two rubber feet are missing. There are scratches. The text "USE BOSS PSA ADAPTOR ONLY" on the power jack is faded. It is an old item, so there is a feeling of use. No claims and no returns, please. AC adapter is not included. Please prepare a BOSS PSA series adapter. - Brand: Roland - Model: MM-4 - Type: MIDI Thru Box - Input Terminals: MIDI IN - Output Terminals: MIDI THRU x 4 - Power: 9V DC IN (BOSS PSA series) - LED Indicators: 2 (Red, Green) Thank you for viewing.