An object of the present invention is to provide an analgesic effective in a prophylactic or a therapy for various pain diseases. The present invention is to provide an analgesic containing at least one member selected from a trans-2-decenoic acid derivative represented by the formula (1) and a pharmaceutically acceptable salt thereof as an active ingredient:(In the formula, Y is —O—, —NR— or —S—, R is hydrogen atom, alkyl group, dialkylaminoalkyl group or the like and W is a substituent such as dialkylaminoalkyl group). The analgesic of the present invention containing the compound as an active ingredient is highly useful as a prophylactic or therapeutic agent for various pain diseases such as the pain caused by osteoarthritis (e.g., knee osteoarthritis and hip osteoarthritis).
