An embeddable sensor (10) includes a sensor body (12), a detector (14) housed in the sensor body (12), and a retaining mechanism (16) mounted on a side surface of the sensor body (12). The retaining mechanism (16) includes at least one projection (22a, 22b) on the side surface of the sensor body (12). The projection (22a, 22b) is of a V shape which is progressively wider and higher from a distal end toward a proximal end of the sensor body (12). The projection (22a, 22b) is made of a material whose hardness is lowered upon elapse of a certain period of time within a living body (S). When the embeddable sensor (10) is inserted in the living body (S), the projection (22a, 22b) retains the embeddable sensor (10) within the living body (S). Upon elapse of the certain period of time within the living body (S), the projection (22a, 22b) loses its capability to retain the embeddable sensor (10) within the living body (S).
