Disclosed an impact detection system including: three or more optical fiber sensors disposed respectively in different positions, the sensors not being in alignment with one another, in which the sensors each includes a core portion to have a grating portion formed therein, the grating portion has a plurality of gratings; light source; two or more optical filters having different pass bands to one another to an output light of one of the optical fiber sensors; and an arithmetic processing apparatus to perform arithmetic processing of output values of the three or more optical fiber sensors through the optical filters so as to specify a position on the subject where an impact is loaded, the output values being obtained when the impact is loaded on the subject.