The present invention provides an in-mold detachable marking device which does not lock rotation of an index body even when the index body is repeatedly rotated to switch marking indications. An in-mold detachable marking device comprises a substantially cylindrical outer shell body for indication fit into a molding mold, an index body fit into the outer shell body for indication and configured to be angularly displaceable around the axis line of the outer shell body for indication, a cover body screwed at the lowermost part of the outer shell body for indication, and a spring which biases the index body with the downward force, said outer shell body for indication and said index body having a marking indication part formed on their surfaces, wherein the index body comprises an index part facing inner surface of the mold, a positioning part extending downward from the index part, and a shaft extending downward from the positioning part, the shaft having a threaded part in its lower part, the spring has an engaging part which engages with the index part, and a fixed part which is fixed to the cover body, pitch of the spring of the engaging part and pitch of the threaded part are equal, and the engaging part and the threaded part engage each other.