It's a volume pedal;  a hefty, smooth, nicely designed, luxurious volume pedal. Doubles as a brick to break windows with.

Model: Boss FV-500H
Made: Taiwan, Feb 2006 (serial G6K3182)
Type: volume
Power: passive, no supply needed
Equivalent new street price (approx): $209aud
Mods: none
Accessories: no box or manual
Condition notes: used, no major marks, fully functional. Overall: very good condition