A vehicle seat and frame thereof which minimize the size of an attachment mechanism of a support structure for supporting the back of a seated person are provided. A seat frame has side frames positioned at right and left sides of a seat back frame and extending in an up to down direction. The side frame has a side portion extending along a side portion of the seat, a rear portion projecting from a rear end of the side portion to an inner side of the seat, and a support member spanned between the right and left side frames, and receives a load of the seated person. The support member has a connecting portion for connecting to the side frame and is attached to the rear portion of the side frame in a state where the positional relationship between the connecting portion and the side frame is fixed.