The present invention relates to a preventive and/or therapeutic agent for spinal canal stenosis comprising aldose reductase inhibitory compounds. A representative example of aldose reductase inhibitory compounds is the compound represented by formula (I):
wherein all the symbols represent the same meaning as described in the specification; a salt of its acid when R
3a
represents hydrogen, or solvate thereof The therapeutic agent of the present invention is effective for prevention and/or therapy for spinal canal stenosis and the like, such as lumbar spinal canal stenosis.