Recently, acquisition of basic count ability has become increasingly valued, but, in many cases, the process is not sufficiently clarified. This study was intended to explore the process of mastering informal mathematics from the viewpoints of situated learning, focusing on the use of fingers during calculation. Questions of one-digit additions such as 2+1, and 3+6, were asked to 15 children aged 5, and their behaviors were observed until they answered. At that time, 3 kinds of objects, cards with numbers, dotted cards as semi-concretion, and marbles as concretion, were presented separately. Additionally, when the children explained how they calculated, their finger movements were also observed. As the result, children used fingers voluntarily on 8% of tasks when adding. Meanwhile, children kept their eyes on a presented object on 14%, which implies that they used their eyes when adding. This tendency became noticeable when a dot card was presented. As for the task for children to explain their calculation methods, children used their fingers on 18% of tasks, and they used their eyes on 5%. These results indicate that preschool children may use their fingers to give explanations to others, but hardly use their fingers as a tool for cognitive processing. Those findings were discussed from an embodied cognition viewpoint.