A stabilizer is a stabilizer including: a main body cylinder portion which is elastically deformable and a pair of connection plate portions respectively connected to a pair of left and right suspension devices, wherein the connection plate portion includes a pair of base material portions located on both sides in the connection plate portion in a plate thickness direction T and an alloy oxide region which is disposed between the pair of base material portions and in which alloy oxides are scattered, and wherein crystal grains constituting the pair of base material portions straddle the alloy oxide region in the plate thickness direction and the pair of base material portions are joined.