A control agent comprising, as an active ingredient, a specific quinoline derivative compound such as 8-fluoro-2,3-dimethyl-6-(1,1-dimethylethyl)-4-(methylcarbonyl)oxyquinoline, azoxystrobin, picoxystrobin, pyraclostrobin, kresoxim-methyl, trifloxystrobin, metominostrobin, orysastrobin, famoxadone, fluoxastrobin, pyribencarb, cyazofamid, amisulbrom, flutolanil, mepronil, isofetamid, fluopyram, carboxin, thifluzamide, fluxapyroxad, furametpyr, penflufen, penthiopyrad, boscalid, diflumetorim, fluazinam, ferimzone, fenpyroximate, or an acid addition salt of any of these compounds shows an excellent controlling effect on Mesostigmata mites.