To provide a semaphorin inhibitor; a peripheral or central nerve regeneration promoter which contains said semaphorin inhibitor as an active ingredient; and a preventive or remedy for a neuropathic disease and a neurodegenerative disease containing said nerve regeneration promoter, or the like.A low-molecular weight compound, which acts at a concentration of 10 .mu.g/ml or below to inhibit the growth cone collapse activity of semaphorin such as semaphorin 3A, semaphorin 6C or the like and/or the nerve outgrowth inhibitory activity of semaphorin in a collagen gel and which does not substantially affect cell proliferation, is obtained from the culture of strain SPF-3059 belonging to the genus Penicillium. The low-molecular weight compound with the semaphorin inhibitory activity thus obtained exhibits the in vivo nerve-regeneration promoting action.