The present invention aims to provide a novel SCD inhibitor.The present invention relate to SCD inhibitor comprising A compound represented by the formula (I) wherein R is an optionally substituted cyclic group or an optionally substituted carbamoyl group, provided that R is not an optionally substituted 7-pyrido[2,3-d]pyrimidyl group; ring A is an optionally further substituted pyridazine ring; R1, R2, R3, R4, R11, R12, R13 and R14 are each independently a hydrogen atom or a substituent, or R1 and R11 in combination, R2 and R12 in combination, R3 and R13 in combination, or R4 and R14 in combination optionally form an oxo group, or R2 and R4 in combination optionally form a bond or an alkylene cross-linkage; m and n are each independently an integer of 0 to 2; ring B is an optionally substituted ring, provided that the two atoms constituting ring B, which are adjacent to the spiro carbon atom, are not oxygen atoms at the same time, or a salt thereof, or a prodrug thereof.