Provided is a radioactive labeled compound that can detect a secondary mutation of an epidermal growth factor receptor and which is a compound represented by Formula (1) described below or a pharmaceutically acceptable salt thereof. In Formula (1), L1 is an alkanediyl group having 1 to 5 carbon atoms or an alkenediyl carbonyl group having 3 to 8 carbon atoms, R1 is a radioactive halogen atom, or 5- to 7-membered monocyclic nitrogen-containing heterocycloalkyl that may have one substituent, R2 is a 6- to 8-membered aryl group or nitrogen-containing heteroaryl group with one substituent, R1 or R2 contains a radioactive halogen atom or a radioactive carbon atom (11C), and Y is -NH- or -O-.
