To provide a construction method for a concrete sidewall and its structure for shortening a construction term and reducing cost of construction as much as possible.

In this construction method for the concrete sidewall 12 having predetermined thickness and height, supporting load of an upper part, and formed by spraying concrete along an underground excavated wall face, ruler members 30 for prescribing a top face part line and an inner face part line of the concrete sidewall 12 are arranged along the underground excavated wall face, and concrete 40 is sprayed into a space prescribed by the ruler members 30 by a plurality of times to fill the space with the concrete in many layers and form the concrete sidewall 12 having the desired shape.