The present invention relates to a novel prostaglandin derivative having an alkynyl group on ?chain, particularly, a novel prostaglandin derivative having a double bond at the 2-position and an alkynyl group on the ?chain and a medicament containing the compound as an active ingredient. According to the present invention, a compound represented by the formula (1) or a pharmaceutically acceptable salt thereof; wherein each symbol is as defined in the present specification, or a cyclodextrin clathrate compound thereof, and a medicament containing the compound as an active ingredient, particularly, a medicament for the prophylaxis or treatment of a blood flow disorder associated with spinal canal stenosis or chronic arterial occlusion, can be provided.