This made in Japan device is a passive antenna tuner, with attenuator. It can be useful to couple wires up to 10 meters, and have some gain especially in upper bands. With longer wires, which load strong signals to the receiver, the Q selector offers attenuation.
The interior looks neat and well constructed, although the variable capacitors look cheap.
It can be used, with different antennas, i.e. loops, wires or the fruit crate loop that follows. By the way, its directivity is not bad.
See also: mizuho uz-77s, active loop antenna