An object of the present invention is to provide a medicament and method for treating lissencephaly patients. The present invention provides a lissencephaly therapeutic or preventive agent comprising a compound represented by the general formula (I): wherein R1 is lower alkyl substituted with lower alkoxy, lower alkyl substituted with a heterocyclic group, a heterocyclic group, or a group represented by the formula (IIa): wherein R4 is lower alkyl, R3 is lower alkylene, and m is an integer of 1 to 6; R2 is lower alkyl optionally substituted with phenyl; and R3 is lower alkyl optionally substituted with halogen, lower alkoxy, or phenyl; condensed polycyclic hydrocarbon; or hydrogen.