Not that light actually. But it feels a hell of a lot lighter than it is since everything is so fluid, no noise, no flex, only what is needed for shock absorption which is the result of a nice, lugged steel frame. What brings the weight up on this bike are the parts. Keep in mind, this is complete keirin bike. Ridden by guys with legs twice as big as your average road rider and with upper body strength. These suckers are monsters who race in a series where contact IS allowed so long as one has two hands on the bars. So, lightness isn't the ultimate goal as much as precision, ride quality and strength. Again, every part on the bike must have an NJS stamp. Sort of like FIA. It means that the part just will not break under any circumstances. So, other than tires and seat (has to be approved as well) nothing on the bike is made out of anything but metal. The bars are chrome-moly and ridiculously stiff. If one needs brakes for street riding, they now make special ones for retired keirin circuit bikes that bolt on to the forks instead of requiring drilling and take into account the tiny tire gaps. Once one understands the mystique of keirin, like rules that require only the rider to work on his own bike, riding the same frame for years, waiting in line to get that frame, the stresses involved, but most of all, riding something some rider made a living on for years instead of some assembly line frame that is some production copy of some tour rider's frame who uses that frame for only a couple of races, one sort of gets a real appreciation for the equipment. Sort of an old school, asian, martial arts style hierarachy translated into a cycling based gambling sport. And the best part is that the equipment mostly has it's roots on Japanese appreciation for classic era italian equipment and all for the best price value in cycling.
http://en.wikipedia.org/wiki/Keirin
http://www.youtube.com/watch?v=k_ONY63vC1U
http://www.youtube.com/watch?v=dFRahWnA4YM