BENZALDEHYDE COMPOUND

PROBLEM TO BE SOLVED: To provide a new compound having folding-promoting action on a mutant rhodopsin, and useful as an active ingredient for a medicine for preventing and/or treating pigmentary degeneration of the retina.SOLUTION: The benzaldehyde compound is represented by formula (I) or a salt thereof. In the formula, Ris an aldehyde group; Rand Rare each hydrogen, hydroxy, alkyl or alkoxy; L, Land Lare each -C(R)(R)- (Rand Rare each hydrogen, hydroxy, halogen or alkyl), -O-, -N(R)- (Ris hydrogen or alkyl) or -C(=Q)- [=Q is =O, =S, =N-R(Ris hydrogen or alkyl) or =C(R)(R) (Rand Rare each hydrogen or alkyl)]; X is -CH-, -CH-CH- or -CH=CH-; Y and Z are each -O-, -CH- or -C(R)(R)- (Rand Rare each hydrogen or alkyl).