Problem Provided is a novel cyanine dye derivative with a pyrazole skeleton and an indole skeleton, having high sensitivity performance in a shorter wavelength region as compared with a conventional optical system, and showing high water solubility.Solution The invention provides (1) a compound represented by the following general formula [50] and a salt thereof: ##STR00001## [wherein R.sup.1 to R.sup.6 each independently represent a substituted or unsubstituted alkyl group which may have an amide bond; R.sup.7 to R.sup.10 each independently represent alkyl group, alkenyl group, alkynyl group, aryl group, alkoxy group, aryloxy group, alkylthio group, arylthio group, alkylsulfonyl group, arylsulfonyl group, carbamoyl group, sulfamoyl group, ureido group or amino group, those groups being able to have substituents; a group represented by the general formula [2]: --COOR.sup.12 [2] (wherein R.sup.12 represents hydrogen atom, C.sub.1 to C.sub.10 alkyl group, alkali metal atom, organic ammonium ion, ammonium ion or anion); a group represented by the general formula [3]: --SO.sub.3R.sup.13 [3] (wherein R.sup.13 represents hydrogen atom, alkali metal atom, organic ammonium ion, ammonium ion or anion), halogen atom, aromatic heterocyclic thio group, hydrogen atom, hydroxyl group, cyano group, formyl group, thiol group or nitro group; R.sup.11 represents hydrogen atom, or alkyl group, alkenyl group, alkynyl group or aryl group, those groups being able to have substituents; and n represents an integer of from 0 to 3, provided that any of R.sup.1 and R.sup.2, R.sup.4 and R.sup.5, R.sup.1 and R.sup.6, and R.sup.2 and R.sup.4 may form a bivalent group with a group selected from --O-- group, --S-- group, --COO-- group and groups represented by the general formulae [52] to [54]: ##STR00002## (wherein R.sup.50 represents hydrogen atom, alkyl group, alkenyl group or aryl group, those groups being able to have substituents), and substituted or unsubstituted alkylene group; and in the case where said bivalent group is formed, at least one of R.sup.1 to R.sup.11, along with the bivalent group formed by any of R.sup.1 and R.sup.2, R.sup.4 and R.sup.5, R.sup.1 and R.sup.6, and R.sup.2 and R.sup.4, has the group represented by the general formula [2], the group represented by the general formula [3], amino group, hydroxyl group, thiol group or formyl group; and in the case where said bivalent group is not formed, at least one of R.sup.1 to R.sup.11 has the group represented by the general formula [2], the group represented by the general formula [3], amino group, hydroxyl group, thiol group or formyl group]; (2) a labeled compound obtained by subjecting the above compound to direct or indirect binding to a substance to be labeled, and (3) a method for labeling a substance to be labeled, comprising subjecting the above compound to direct or indirect binding to the substance to be labeled.