The purpose of the present invention is to stably retain a posture of a subject or patient when carrying out a medical procedure such as diagnosis or treatment. Provided is a medical posture retaining mat, comprising an airtight bag (2) and a shape retaining layer (3). The airtight bag (2) is a cover of the posture retaining mat (1) which sustains a posture of a human body. The shape retaining layer (3) is an interior material of the mat (1) contained within the airtight bag (2), is formed by the stacking of granules (P) having adhesive surfaces, is plastically deformable at room temperature, deforms in response to an external force being applied thereto, and retains the shape of said deformation. The shape retaining layer (3) is deformed prior to use in the shape of a specific part of the human body which is to be immobilized in place, a neck part receiving furrow (5) and a head part receiving depression (6), for example, which are concave parts of the deformed mat, then receive the head part (H) and neck part (N) of a human body, and the interior of the airtight bag (2) is degassed so as to harden the mat (1), immobilizing the head part of the subject or patient and stably retaining a given posture during a diagnosis or an operation.
