Hi Shinichiro,
Here's the details about your bass:
RSB4 Rokkomann 4-string bass
top: Zebrawood
accent: Maple laminate
body: Mahogany
neck: 3-piece Maple with 2 Walnut pinstripes
scale: 30.75 short
fingerboard: Ebony
inlays: Pearloid (plastic) ovals
pickup: 1 AXY
controls: volume, filter, Q switch, mono output
finish: satin rubout
originally made for Rokkomann, Inc., Kobe, Japan
birthday: October 28, 1993
Rokkomann, Inc. was our distributor in Japan for many years. They wanted to have a lower priced short scale bass to offer since the Stanley Clarke models were so popular in Japan. I don't have any records of the exact number made, but my guess is less than 30 pieces.
It's not considered a Stanley Clarke model, though the body shape and scale length are the same as a Stanley Clarke model.
There are also 3/4 Spoiler models, but this bass is not one of them.