To provide a design method for an external structural approach through which one can safely come and go while leaving a space without imparting scantiness.

In the design method, an external structural approach pattern corresponding to an arrangement space in a site is selected from a plurality of external structural approach patterns. In an external structural approach pattern provided with a lateral entry type gate (2), the width (W5) of the space (31) in front of the gate is kept to have at least 2,000 mm, the depth (Z4) is kept to have at least 2,200 mm, the width (W6) of the opened space (33) of the gate door (32) is kept to have at least 2,000 mm, the depth (W6) of the opened space (33) of thegate door (32) is kept to have at least 1,000 mm, and further, an allowable space (34) as wide as at least 300 mm in the width (W7) is given in the depth side.