An amyloid fibril formation inhibitor comprising a compound represented by the following general formulae (I) to (III): wherein Q is —C(═O)—; X is —C(═O)—, —NH—C(═O)—; Y is —(CH2)m—; Z is —(CH2)n—; R1, R2, and R3 are each independently a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkylaminoalkyl group; and R4 is an amino group, an alkylamino group or the like; or a pharmaceutically acceptable salt thereof or a solvate thereof.