A pH-sensitive micelle comprising a compound which is an anti-cancer agent, wherein the anti-cancer agent is a compound having an indolocarbazole backbone, and an epirubicin-conjugated copolymer, in which epirubicin or a salt thereof is bound to a block copolymer represented by the following Chemical Formula or Chemical Formula via hydrazide groups of the block copolymer, and wherein as a result of binding epirubicin or salt thereof, units having a hydrazide group in a side chain account for more than 0% to no more than 35% of the total number of polyamino acid units in the block copolymer: or wherein, R 1, which may be the same or different, represents a hydrogen atom, methoxy group, methyl group, substituted linear, branched or cyclic C 1 -C 12 alkyl group, in which the substituent is a functional group selected from the group consisting of a maleimido group, amino group, carboxyl group, thiol group, hydroxyl group and active ester group, which may be protected, R 2 represents a hydrogen atom, saturated or unsaturated C 1 -C 30 aliphatic carbonyl group or arylcarbonyl group, R 3 represents -O-R 5 or -NH-R 5 in which R 5, which may be the same or different, represents a hydrophobic group, R 4 represents a hydroxyl group, saturated or unsaturated C 1 -C 30 aliphatic oxy group or aryl-lower alkyloxy group, L 1 and L 2 independently from each other represents a linker, m represents an integer of 5 to 1000, n represents an integer of 0 to 1000, p represents an integer of 1 to 1000, q represents an integer of 1 to 1000, provided that in the case units having a hydrophobic group in a side chain thereof account for 25% to 75% of the total number of polyamino acid units in the block copolymer and units having a carboxylic acid group are present in a side chain thereof, units having a carboxylic acid group in a side chain thereof, units having a hydrophobic group in a side chain thereof and units having a hydrazide group in a side chain thereof are randomly distributed throughout the entire polyamino acid region, while in the case units having a carboxylic acid group in a side chain thereof are not present, units having a hydrophobic group in a side chain thereof and units having a hydrazide group in a side chain thereof are randomly distributed throughout the entire polyamino acid region, and y represents an integer of 1 or 2. R 1, which may be the same or different, represents a hydrogen atom, methoxy group, methyl group, substituted linear, branched or cyclic C 1 -C 12 alkyl group, in which the substituent is a functional group selected from the group consisting of a maleimido group, amino group, carboxyl group, thiol group, hydroxyl group and active ester group, which may be protected, R 2 represents a hydrogen atom, saturated or unsaturated C 1 -C 30 aliphatic carbonyl group or arylcarbonyl group, R 3 represents -O-R 5 or -NH-R 5 in which R 5, which may be the same or different, represents a hydrophobic group, R 4 represents a hydroxyl group, saturated or unsaturated C 1 -C 30 aliphatic oxy group or aryl-lower alkyloxy group, L 1 and L 2 independently from each other represents a linker, m represents an integer of 5 to 1000, n represents an integer of 0 to 1000, p represents an integer of 1 to 1000, q represents an integer of 1 to 1000, provided that in the case units having a hydrophobic group in a side chain thereof account for 25% to 75% of the total number of polyamino acid units in the block copolymer and units having a carboxylic acid group are present in a side chain thereof, units having a carboxylic acid group in a side chain thereof, units having a hydrophobic group in a side chain thereof and units having a hydrazide group in a side chain thereof are randomly distributed throughout the entire polyamino acid region, while in the case units having a carboxylic acid group in a side chain thereof are not present, units having a hydrophobic group in a side chain thereof and units having a hydrazide group in a side chain thereof are randomly distributed throughout the entire polyamino acid region, and y represents an integer of 1 or 2.