PROBLEM TO BE SOLVED : To provide a pharmaceutical that can be orally administered, and has less side effect, higher safety, and excellent effectiveness and pharmacokinetic properties, and contains a compound useful for a blood flow improver, especially, a therapeutic agent for a blood flow disorder and pain caused by spinal stenosis, as an active ingredient. SOLUTION : The present invention provides a compound of formula 1 [RA : -CH=CZ1(COX) or the like; Z1 : H or the like; X : OR4 or the like; R4 : H or the like; Y : S or the like; A-B : a carbon-carbon single bond or the like; a hydroxy group bound by a wave line : a hydroxy group such as α-arrangement; R1, R2 : independently H or the like; n is an integer of 0-2; R3 is a C2-3 alkyl group or a C3-5a cycloalkyl group]. SELECTED DRAWING : None COPYRIGHT : (C)2019, JPO&INPIT