A biaxially oriented blow-molded bottle-shaped container made of synthetic resin comprises a rectangular tubular body provided with a generally central circumferential groove having upper and lower sidewalls. The sidewalls are inclined at an oblique angle within a range of 21.degree.-28.degree. with respect to a vertical longitudinal axis of the container. The rectangular tubular body includes flat walls, each having a central recessed portion with a bottom wall comprising a shaped panel wall for compensating for deformation due to reduced pressure in the container and a shaped peripheral groove invertedly curved around the shaped panel wall. The shaped panel wall has ribs traversing the shaped panel wall parallel to each other, and a crest of each of the ribs has a larger radius of curvature than that of a root thereof. The rectangular tubular body has an upper end which is a regular polygon having twice as many corners as corner panels of a main portion of the body and a shoulder having a lower end portion connected to the upper end of the body. The lower end portion of the shoulder is in the form of a regular polygonal truncated pyramid shape.