Provided are a gas separation membrane which has a resin layer containing a compound having a siloxane bond, in which the resin layer containing a compound having a siloxane bond satisfies Expressions 1 and 2, and at least one of gas permeability or gas separation selectivity is high under high pressure; a method of producing a gas separation membrane; a gas separation membrane module; and a gas separator. 0.9≧A/B≧0.55  Expression 1 B≧1.7  Expression 2 In the expressions, A represents an O/Si ratio that is a ratio of the number of oxygen atoms relative to the number of silicon atoms contained in the resin layer containing a compound having a siloxane bond at a depth of 10 nm from the surface of the resin layer containing a compound having a siloxane bond, and B represents an O/Si ratio that is a ratio of the number of oxygen atoms relative to the number of silicon atoms in the surface of the resin layer containing a compound having a siloxane bond.