This is a vintage Ibanez Phantom Power Unit manufactured in Japan between 1977 and the early 1980s. 

It was designed to power active electronics in specific Ibanez guitars (like the Artist 2622 or 2700P) via a stereo cable, eliminating the need for a 9V battery inside the instrument. 

The unit converts AC wall power into 9V DC power, featuring a red LED indicator and dedicated jacks for both "AMP" and "GUITAR" connections. 

The unit was introduced for 1977 along with the Artist 2622 and was later sold with some other models. It works without modification with any active EQ model wired with an LED (e.g. AR500, MC550, AR5000, 2700). Other models from the Artist, Musician and Studio series may need to be rewired to work with the phantom power unit. 

The advantage of the phantom power unit is that it obviates the need for an onboard power sources (typically a 9V battery) to provide power to the active EQ circuit. This eliminates the possibility of having a battery die mid-performance which would impact the tone of the instrument. It also ensures the circuit is fed with a constant voltage level - the voltage provided by a battery can decrease as the battery is depleted.