A back support cushion device includes a support member, at least one cushion assembly, and at least one elastic assembly. The support member includes a first groove. The cushion assembly includes a second groove. The elastic assembly is located between the support member and the cushion assembly and includes an elastic member, and first and second members. The elastic member includes first and second portions. The first portion is engaged into the first groove, and the second portion is engaged into the second groove. The first member includes a first end disposed in the first portion and a second end connected to the first groove. The second member includes a first end disposed in the second portion and a second end connected to the second groove.