To provide a compound for a probe used as an early and accurate image diagnosis of diseases caused by τ-protein accumulation, a composition and kit containing the compound, also method for staining the change of neurofibril in a brain specimen and a medicinal composition for the prevention/treatment of diseases to which the β-sheet structure of the protein becomes the cause of the diseases or a part of the causes.

This compound expressed by the formula [wherein, R1, R2 are each independently H, a halogen, OH or a 1-4C alkyl; R3, R4 are each independently H or a 1-4C alkyl; and (m), (n) are each an integer of 0-4] or its salt or solvated compound can be used as image diagnosis probes of the diseases of accumulating τ-protein.