An upper arm module of a wearable muscular strength assisting apparatus is provided. The upper arm module includes a base part configured to be connected to a wearer's body, and an upper arm part having a first end thereof coupled to the base part to be rotatable about a fixed point. The upper arm part is coupled to the wearer's upper arm to apply a torque thereto. The upper arm module further includes an elastic body having a first end thereof fixedly coupled to the upper arm part and generating an elastic force by deformation. In particular, the upper arm module also includes a first link having a first end thereof rotatably coupled to the base part at a point of application, and a second link rotatably coupled to the second end of the first link at a first point.