To provide a fully portable collapsible bathtub provided with the degree of freedom in the selection of an installation place.

A peripheral wall (2) in a square tubular shape is formed by connecting front and back surface plates (5, 6) bendable at a horizontal center part to both end parts of unbendable left and right side plates (3, 4) so a to be turnable and at least the front surface plate (5) so as to be attachable and detachable. An outer container (1) in a blind square tubular shape is formed by mounting the peripheral wall (2) on a bottom plate (7) rectangular in the plane view. Also, a control body (10) controlling the outward movement of the peripheral wall (2) is provided on the outer peripheral edge part of the bottom plate (7). An inner container (12) formed in the blind square tubular shape with a water non-permeable sheet is attachably and detachably housed inside the outer container (1). For the inner container (12), at least a front surface sheet (12c) is connected by a connector (13) with a watertight function separably from each other.