The computer for scuba diving is necessary equipment for safety dive. And it computes inhalation or discharge of the nitrogen by the experence learning which causes decompression sickness.Usual dive computer is big, so people we ars it only when people dive. However, weachieved "wearable computer" which provides the safety function, by using saving technology of watch. The deveropment makes it small, makes it possible to carry always and takes in the information of individual. I describe about outline of watch size computer for scuba diving, which we developed for the first time in the world, in this paper.