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

Model: Boss FV500L
Made: Taiwan, recent model
Type: volume
Power: passive, no supply needed
Draw: n/a
Switching: n/a
Dimensions, excluding knobs/switches/jacks: 270x100x65 
Equivalent new street price (approx): $159 approx
Mods: velcro added
Accessories: no box or manual
Condition notes: used, few minor marks, good condition

Controls
Minimum volume: sets the low threshold for when the pedal is fully down