It's a volume pedal;  a hefty, smooth, nicely designed, luxurious volume pedal. It also looks like it came straight from the Star Trek universe.

Model: Boss FV-500H
Made: Taiwan, August 2019
Serial: H5K8652
Type: volume
Power: passive, no supply needed
Equivalent new street price (approx): $209aud
Mods: none
Accessories: original box and manual
Condition notes: used, no major marks, fully functional. Overall: very good condition