I investigate the fragmentation under high frequency trading (HFT) popularity. I make a toy model of security exchange market competition. With the friction like the Bertrand competition with differentiated goods, the effect of the number of venues on bid ask spread depends on the business stealing effect. Using Nikkei 225 future's data and focusing on the system down of Singapore Exchange as a natural experiment, I show the smaller number of venues means larger bid ask spread. When we think about welfare loss both from HFT investment and the effect of bid ask spread, the relationship between the number of venues and welfare is vague.