[Problem] To provide a novel proteasome inhibitor which can be administered orally. [Solution] A proteasome inhibitor comprising, as an active ingredient, a compound represented by general formula (1) [wherein Y and Y' are the same as or different from each other and independently represent a single bond, -O-, -NH-, -CH=CH?, -CO-CH=CH?, -O-CONH?, -S-CO?, -CONH?, -NHCO? or NHSO2? [wherein "?" represents a bond located on the phenyl group side]
R1, R2, R3, R4, R5, R6, R7 and R8 are the same as or different from one another and independently represent a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a carboxyl group, a C1-6 alkyl group, a C1-6 alkoxy group or a C1-6 alkoxycarbonyl group
R9 and R10 are the same as or different from each other and independently represent a hydrogen atom or a C1-6 alkyl group, or R9 and R10 together form -CH2CH2- or -CH2CH(R11)CH2- [wherein R11 represents a hydrogen atom, a C1-6 alkoxy group or a C1-6 alkylsulfonyloxy group]
and m and n are the same as or different from each other and independently represent an integer of 2-4] or a salt thereof, or a solvate of the compound or the salt.