A radioactive isotope-labeled dye compound represented by the following general formula (I):wherein R1 and R2 represent a substituent, R3 to R6 represent a substituted or unsubstituted alkyl group R7 and R8 represent a substituted or unsubstituted alkyl group L1 to L3 represent a substituted or unsubstituted methine group r represents an integer of 0 to 3 P and Q represent 123I, 124I, 125I, 131I or 18F M represents hydrogen atom, Na, or K and m and n represent an integer of 0 to 2.