A square bottle that includes a mouth portion, a shoulder portion, a body portion, and a bottom portion provided to be continuous in this order from the top to the bottom in a bottle axis direction, wherein in the body portion a plurality of panel surface portions are provided to be continuous with each other with corner portions therebetween in a circumferential direction around a bottle axis and in the body portion a first peripheral groove straddling at least the corner portions in the circumferential direction is formed, and a ridge portion straddling the corner portions in the circumferential direction is formed on an inner surface defining the first peripheral groove.