To providing a space truss assembling method for unitizing a space truss into minimum kinds of units of the same shape for simplifying a unit manufacturing process in a plant and work in a constructing field.

In a first truss unit 1A, upper chord members 2, 2, etc., forming a rectangle in the plane view are connected together only in the diagonal direction by means of upper connection apparatuses 5 and 5, while upper diagonal corners of pyramidal diagonal members 4, 4, etc., assembled at the lower panel joints by means of a lower connection apparatus 6 are connected to the upper connection apparatuses 5 and 5. The first truss unit 1A, a second truss unit 1B, which is the first truss unit 1A turned by 90 degrees around the vertical axis, and a third truss unit 1C constructed of pyramidal diagonal members 4, 4, etc., assembled at the lower panel joints by means of the lower connection apparatus 6 are arranged alternately and connected to be assembled together via lower chord members 3, 3, etc., connecting the lower connection apparatuses 6 and 6 together.