A pen pressure detecting module comprising: a first holder; a second holder; and a pressure sensing device including a first electrode, and a second electrode disposed so as to be opposed to the first electrode at a predetermined distance from the first electrode, a capacitance being formed between the first electrode and the second electrode, the pressure sensing device sensing a pressure applied to the second holder that is transmitted to the first electrode based on a change in the capacitance, the change in the capacitance being caused by a displacement of the first electrode in correspondence with the pressure; the first holder having a hollow portion formed with a cylindrical inner shape, the second holder being housed in the hollow portion, and the pressure sensing device being disposed so as to sense the pressure applied to the second holder that is transmitted to the first electrode; the second holder having an engaging portion to be engaged with a pressure transmitting member to which the pressure is applied, wherein the engaging portion of the second holder has a recessed portion into which the pressure transmitting member is inserted in an axial direction of the second holder, and a locking portion that detachably locks the pressure transmitting member to the second holder and that is provided in an inner circumferential surface of the recessed portion, wherein the locking portion provided in the inner circumferential surface of the recessed portion has a projecting portion or a dent portion, the pressure transmitting member has a dent portion or a projecting portion corresponding to the projecting portion or the dent portion of the locking portion at a predetermined position inserted into the recessed portion, the pressure transmitting member is inserted into the recessed portion, and the second holder is locked to the pressure transmitting member while the projecting portion or the dent portion of the locking member is engaged with the dent portion or the projecting portion of the pressure transmitting member. a first holder; a second holder; and a pressure sensing device including a first electrode, and a second electrode disposed so as to be opposed to the first electrode at a predetermined distance from the first electrode, a capacitance being formed between the first electrode and the second electrode, the pressure sensing device sensing a pressure applied to the second holder that is transmitted to the first electrode based on a change in the capacitance, the change in the capacitance being caused by a displacement of the first electrode in correspondence with the pressure; the first holder having a hollow portion formed with a cylindrical inner shape, the second holder being housed in the hollow portion, and the pressure sensing device being disposed so as to sense the pressure applied to the second holder that is transmitted to the first electrode; the second holder having an engaging portion to be engaged with a pressure transmitting member to which the pressure is applied, wherein the engaging portion of the second holder has a recessed portion into which the pressure transmitting member is inserted in an axial direction of the second holder, and a locking portion that detachably locks the pressure transmitting member to the second holder and that is provided in an inner circumferential surface of the recessed portion, wherein the locking portion provided in the inner circumferential surface of the recessed portion has a projecting portion or a dent portion, the pressure transmitting member has a dent portion or a projecting portion corresponding to the projecting portion or the dent portion of the locking portion at a predetermined position inserted into the recessed portion, the pressure transmitting member is inserted into the recessed portion, and the second holder is locked to the pressure transmitting member while the projecting portion or the dent portion of the locking member is engaged with the dent portion or the projecting portion of the pressure transmitting member.