Previous research has demonstrated that both hearing adults and hearing children with no training in arithmetic successfully performed approximate arithmetic on large sets of elements. Here, the possibility is explored that the same phenomenon can be confirmed in deaf adults who have acquired a signed language as their first language. Results reveal that they can perform simple arithmetic subtraction on nonsymbolic numerosities. Their performance levels were even higher than those of hearing adults who participated in the experiment as a control group. On the other hand, the performance levels of subtraction of the deaf adults in the formal mathematics were lower than those of the hearing adults. The findings are argued in terms of the characteristics of cognitive capabilities the deaf adults acquired through their development.