Abstract: A fuel-tank control valve includes: casing; main float; plate with upper surface that constitutes bottom portion of casing, and that includes first gas-storage chamber formed of plate and peripheral wall portion that is provided upright from rim of upper surface to lower side; sub float arranged above the plate; second gas-storage chamber formed of a part including gas supply hole of first gas-storage chamber among parts of upper surface, and partition-wall portion which is away from peripheral wall portion, and that is provided in first gas-storage chamber; and clearance which is formed between casing and peripheral wall portion, and through which fuel in fuel tank can flow in, second gas-storage chamber and clearance being provided for sub float. Upper surface includes protruding seating portion that forms inflow space through which gas through gas supply hole can flow in under state in which sub float is seated on protruding seating portion.