The present invention provides a therapeutic and/or prophylactic medicament for FGFR3 diseases, the medicament comprising a HMG-CoA reductase inhibitor as an active ingredient; a method for treating and/or preventing FGFR3 diseases, the method comprising administering a HMG-CoA reductase inhibitor; use of a HMG-CoA reductase inhibitor in the production of a therapeutic and/or prophylactic medicament for FGFR3 diseases; and a method for screening for a therapeutic and/or prophylactic drug for FGFR3 diseases.