This textbook demonstrates theoretical principles and actual cases of structural mechanics. This book explains basic definitions of beam, frame, and truss which are widely used in the field of structure mechanics and also shows important engineering tests such as moment distribution, characteristics of member section, analysis of a truss, analysis of a statically indeterminate structure, and principle of bending resistance of concrete section. These contents can help many students to figure out the resistance principle of a structure through simple model tests, dynamics, reinforced concrete structure, steel frame structure and understand how dynamic computational equation is mathematically used in structure mechanics.