A control rod comprising a blade unit structured by arranging a neutron absorbing material in a sheath member having a U-shaped cross section, a lower part support member attached at the lower end of said blade unit, a handle unit which is arranged in a through hole provided in said lower part support member, connected to said lower part support member on the left and right sides, and can slide in the axial direction of said control rod, a coupling socket unit in which a connector of a control rod drive unit is inserted, and a lock plug which is arranged in said coupling socket unit, connected to said handle unit, extended in said axial direction, and connects or disconnects said connector and said coupling socket unit by operating said handling unit, wherein grooves are made in the left and right sides of said handle unit, and thin parts are formed on the left and right sides of said lower part support member facing on said through hole over the sliding range of said handle unit respectively, and said left and right thin parts are inserted individually in said left and right grooves respectively so as to connect said handle unit to said lower part support member, and in the perpendicular direction to said axial direction, a first gap formed between the end of one thin part and the bottom of said groove in which said end is inserted is larger than a second gap formed between the end of said other thin part and the bottom of said groove in which said end is inserted.