To make compatible both the reduction of the weight of a container and the maintenance of a fastening force of a cap, relating to a synthetic resin container and a method for attaching the cap to the container.

The synthetic resin container 10 includes: an extrusion port 21 from which a content is extruded; a neck 20 disposed at an upper part of the extrusion port when the extrusion port 21 is upside, and having a male screw 22 formed around an outer periphery of the neck; and a flexible container body 30 disposed at a lower part of the neck 20 when the extrusion port 21 is upside to store the content therein. The container body 30 has a depression part 31 formed by depressing an outer surface of the container body by protruding an inner surface of the container body 30 at a position adjacent to the neck 20.