1. A wearable apparatus for measuring position and action of an arm, comprising: a main frame worn on an upper body of a user; and an arm motion-measuring unit connected to a side of the main frame, having a plurality of joints and a plurality of arm members, and worn on an arm of a user, wherein at least one of the plurality of arm members of the arm motion-measuring unit has a straight-motional degree of freedom, and wherein a straight-moving unit having the plurality of arm members includes: a first straight-moving frame; a second straight-moving frame having a first side to which the first straight-moving frame is longitudinally movably coupled; and a third straight-moving frame longitudinally movably coupled to a second side of the second straight-moving frame.