Concrete pieces falling from tunnel lining are extremely dangerous for highway traffic. The purpose of this study is to quantify the danger of exfoliation of concrete fragment. Crack condition of lining concrete in 7 tunnels was investigated in order to obtain the fundamental properties of exfoliation. Cracks in lining were defined as 3 types by its directions, and investigated cracks were categorized by these crack types. The influence factors on exfoliation are investigated from various crack data.