In the PART I of this paper, a new concept for the one-dimensional deployable truss structure is presented. The deployed configuration of the structure consists of the repetition of an octahedral truss module longitudinally, and thus it is exactly the so-called "geodesic beam" structure. The principal mechanical feature of the truss is that the lateral members comprising the lateral triangular truss are telescoping beams. Contracting of the lateral members results in the deployment of the truss structure. The geometric transformation of this truss of variable geometry is presented. It is shown that both simultaneous and sequential modes of transformation are possible. The validity of the transformation applied to the deployment is verified through design of a conceptual model. In the PART II of the paper, a preview is presented as for the applications of the concept to a curvilinear truss and a space manipulator arm. 資料番号: SA0034982000