Abstract: The present invention provides a novel sulfonamide compound having a ribonucleotide reductase inhibitory activity or a salt thereof, and a pharmaceutical composition containing the same as an active ingredient. A compound represented by Formula (I) [wherein, X1 represents an oxygen atom or the like; X2 represents an oxygen atom; X3 represents —NH—; X4 represents a hydrogen atom or the like; R1 represents —C(R11)(R12)— or the like; R11 and R12 are the same or different and each represents a hydrogen atom or the like; R2 represents an optionally substituted C6-C14 aromatic hydrocarbon group or the like; R3 represents an optionally substituted C6-C14 aromatic hydrocarbon group or the like; R4 represents a hydrogen atom or the like] or a salt thereof.