A shoulder harness for a portable work machine comprising: a back member that is to be located on a back of an operator, said back member including a main frame, to which a downward extension frame connected with a waist belt is detachably attached; right and left shoulder belts (104R, 104L) that respectively extend from right and left upper end portions of said back member; a joint buckle that is to be located on a chest of said operator, distal ends of said right and left shoulder belts (104R, 104L) being connected to said joint buckle; a hip pad that is to be located on a side of a waist of said operator, and is provided with a locking device, to which a work machine is to be connected; a relay member that is located above said locking device, and is connected to said locking device by a hanging member; a rear suspension belt that is connected to said relay member and said back member; and a front suspension belt that is connected to said relay member and said joint buckle, wherein a mechanism for attaching and detaching said downward extension frame to and from said main frame includes a first shape portion (186, 188) formed in said main frame, and a second shape portion (196, 198) formed in said downward extension frame, and said downward extension frame is attachable to and detachable from said main frame by engagement and disengagement between said first and second shape portions (186, 188, 196, 198), characterized in that said hanging member is composed of a band-like belt whose length is adjustable. wherein an armpit belt is detachably attached to said main frame, said armpit belt extending along an armpit on one side of said operator from said main frame and a distal end of said armpit belt being connected to said joint buckle. a back member that is to be located on a back of an operator, said back member including a main frame, to which a downward extension frame connected with a waist belt is detachably attached; right and left shoulder belts (104R, 104L) that respectively extend from right and left upper end portions of said back member; a joint buckle that is to be located on a chest of said operator, distal ends of said right and left shoulder belts (104R, 104L) being connected to said joint buckle; a hip pad that is to be located on a side of a waist of said operator, and is provided with a locking device, to which a work machine is to be connected; a relay member that is located above said locking device, and is connected to said locking device by a hanging member; a rear suspension belt that is connected to said relay member and said back member; and a front suspension belt that is connected to said relay member and said joint buckle, wherein a mechanism for attaching and detaching said downward extension frame to and from said main frame includes a first shape portion (186, 188) formed in said main frame, and a second shape portion (196, 198) formed in said downward extension frame, and said downward extension frame is attachable to and detachable from said main frame by engagement and disengagement between said first and second shape portions (186, 188, 196, 198), characterized in that said hanging member is composed of a band-like belt whose length is adjustable. wherein an armpit belt is detachably attached to said main frame, said armpit belt extending along an armpit on one side of said operator from said main frame and a distal end of said armpit belt being connected to said joint buckle.