A physical quantity measuring device, which is a pressure measuring device, a temperature measuring device, or a differential pressure measuring device, wherein the physical quantity measuring device comprises: a cylindrical case whose circumferential portion is provided with a through-hole; a sensor module housed in the cylindrical case and configured to detect a physical quantity; a joint attached with the sensor module, the joint being disposed to cover a first opening of the cylindrical case; a lid member disposed to cover a second opening of the cylindrical case; a circuit board comprising an electronic circuit configured to receive a signal detected by the sensor module and an electronic adjuster configured to adjust the electronic circuit, the circuit board being housed in the cylindrical case; a cap member configured to be attached to cover the through-hole; and a sealing member configured to provide a seal between the through-hole and the cap member, wherein the electronic adjuster comprises an operable portion disposed at a position corresponding to the through-hole, the lid member comprises a circuit-board support supporting the circuit board and an attachment target portion for the cap member to be detachably attached, the cap member comprises a cap member body disposed outside the cylindrical case and configured to cover the through-hole, a cap member shaft extending from a bottom surface of the cap member body, and a cap member engagement portion extending from an end of the cap member shaft in a radial direction of the cap member shaft, characterised in that the sealing member comprises an annularly-shaped sealing member body surrounding the cap member shaft, a linear member extending from the sealing member body, and a sealing-member engagement portion provided at an end of the linear member, the attachment target portion comprises: a shaft insertion hole into which the cap member shaft is insertable; an engagement-portion insertion hole (541B, 541C) into which the cap member engagement portion is insertable, the engagement-portion insertion hole (541B, 541C) being continuous with the shaft insertion hole; and a groove in which the linear member is rested, the groove being continuous with the shaft insertion hole, the cap member is pivotally supported by the attachment target portion to be rotatable to take a first orientation and a second orientation, the cap member engagement portion being insertable into the engagement-portion insertion hole (541B, 541C) in the first orientation and engageable with the attachment target portion in the second orientation, and in the first orientation, the linear member is located in a region in a rotation direction from the first orientation to the second orientation with respect to the cap member engagement portion as viewed in a direction of the cap member shaft. a cylindrical case whose circumferential portion is provided with a through-hole; a sensor module housed in the cylindrical case and configured to detect a physical quantity; a joint attached with the sensor module, the joint being disposed to cover a first opening of the cylindrical case; a lid member disposed to cover a second opening of the cylindrical case; a circuit board comprising an electronic circuit configured to receive a signal detected by the sensor module and an electronic adjuster configured to adjust the electronic circuit, the circuit board being housed in the cylindrical case; a cap member configured to be attached to cover the through-hole; and a sealing member configured to provide a seal between the through-hole and the cap member, wherein the electronic adjuster comprises an operable portion disposed at a position corresponding to the through-hole, the lid member comprises a circuit-board support supporting the circuit board and an attachment target portion for the cap member to be detachably attached, the cap member comprises a cap member body disposed outside the cylindrical case and configured to cover the through-hole, a cap member shaft extending from a bottom surface of the cap member body, and a cap member engagement portion extending from an end of the cap member shaft in a radial direction of the cap member shaft, characterised in that the sealing member comprises an annularly-shaped sealing member body surrounding the cap member shaft, a linear member extending from the sealing member body, and a sealing-member engagement portion provided at an end of the linear member, the attachment target portion comprises: a shaft insertion hole into which the cap member shaft is insertable; an engagement-portion insertion hole (541B, 541C) into which the cap member engagement portion is insertable, the engagement-portion insertion hole (541B, 541C) being continuous with the shaft insertion hole; and a groove in which the linear member is rested, the groove being continuous with the shaft insertion hole, the cap member is pivotally supported by the attachment target portion to be rotatable to take a first orientation and a second orientation, the cap member engagement portion being insertable into the engagement-portion insertion hole (541B, 541C) in the first orientation and engageable with the attachment target portion in the second orientation, and in the first orientation, the linear member is located in a region in a rotation direction from the first orientation to the second orientation with respect to the cap member engagement portion as viewed in a direction of the cap member shaft.