The invention relates to a compound of a general formula (I): wherein A1 and A2 each mean a nitrogen atom or an optionally-substituted methine group; Ring B means a 5-membered to 7-membered aliphatic ring, or a spiro or bicyclo ring formed from the aliphatic ring and any other 3-membered to 7-membered aliphatic ring; R1 means a hydrogen atom, or an optionally-substituted C1-C6 alkyl group, or an optionally-substituted aryl, aralkyl or heteroaryl group; R2 means an optionally-substituted aryl, aralkyl or heteroaryl group; and X means a group of ═NH or ═O, etc. Based on its excellent Wee1 kinase-inhibitory effect, the compound of the invention has cell growth-inhibitory effect and has an additive/synergistic effect with any other anticancer agent, and is therefore useful in the field of medicine.