A biaxially stretched, blow molded synthetic resin bottle with a bottom having a function for absorbing depressurization caused by cooling the bottle after it has been hot-filled with a content fluid, comprising: a bottom plate of the bottom, a peripheral foot disposed around an outermost border of the bottom plate of the bottom, and a deformable sunken portion of the bottom disposed inside of the peripheral foot, said deformable sunken portion comprising: a bottom ridge disposed inward from the peripheral foot and formed by projecting a portion of the bottom plate downward to a position lower than a level of the peripheral foot so that the bottom ridge performs a function as a ground contact portion, and a central concave portion formed at a center of the bottom plate by concaving the bottom plate upward and inward by way of a step which plays the role of a circular rib, starting from an edge of an inner sidewall of the bottom ridge, wherein: the bottom ridge draws fully upward to a position higher than the level of the peripheral foot when the deformable sunken portion draws upward to perform a satisfactory vacuum absorbing function with progress of internal depressurization, and in this state, the peripheral foot instead of the bottom ridge is assigned to perform the function as the ground contact portion, characterised in that the trapezoidal or U-letter shape of the bottom ridge is allowed to extend so that the deformable sunken portion draws upward smoothly and the bottom ridge in the trapezoidal cross-sectional shape deforms in an extending manner. a bottom plate of the bottom, a peripheral foot disposed around an outermost border of the bottom plate of the bottom, and a deformable sunken portion of the bottom disposed inside of the peripheral foot, said deformable sunken portion comprising: a bottom ridge disposed inward from the peripheral foot and formed by projecting a portion of the bottom plate downward to a position lower than a level of the peripheral foot so that the bottom ridge performs a function as a ground contact portion, and a central concave portion formed at a center of the bottom plate by concaving the bottom plate upward and inward by way of a step which plays the role of a circular rib, starting from an edge of an inner sidewall of the bottom ridge, wherein: the bottom ridge draws fully upward to a position higher than the level of the peripheral foot when the deformable sunken portion draws upward to perform a satisfactory vacuum absorbing function with progress of internal depressurization, and in this state, the peripheral foot instead of the bottom ridge is assigned to perform the function as the ground contact portion, a bottom ridge disposed inward from the peripheral foot and formed by projecting a portion of the bottom plate downward to a position lower than a level of the peripheral foot so that the bottom ridge performs a function as a ground contact portion, and a central concave portion formed at a center of the bottom plate by concaving the bottom plate upward and inward by way of a step which plays the role of a circular rib, starting from an edge of an inner sidewall of the bottom ridge, wherein: the bottom ridge draws fully upward to a position higher than the level of the peripheral foot when the deformable sunken portion draws upward to perform a satisfactory vacuum absorbing function with progress of internal depressurization, and in this state, the peripheral foot instead of the bottom ridge is assigned to perform the function as the ground contact portion, the bottom ridge draws fully upward to a position higher than the level of the peripheral foot when the deformable sunken portion draws upward to perform a satisfactory vacuum absorbing function with progress of internal depressurization, and in this state, the peripheral foot instead of the bottom ridge is assigned to perform the function as the ground contact portion,