A pressure detection device comprising: a pressure detection unit configured to detect a pressure transmitted to a pressure detecting surface; a flow passage unit in which a flow passage configured to cause a fluid to flow in a flow direction from an inflow port to an outflow port and a pressure transmitting surface used for transmitting, to the pressure detecting surface, a pressure of a fluid flowing through the flow passage are formed; and a mounting unit used for removably mounting the flow passage unit on the pressure detection unit, wherein the pressure detection unit includes a body, a sensor unit having the pressure detecting surface, characterized in that the pressure detection device further comprises: a holding unit configured to hold the sensor unit movably along an axis orthogonal to the pressure detecting surface, and an urging unit configured to generate urging force to urge the sensor unit toward the pressure transmitting surface, the urging unit comprising a spring and a base member, wherein the spring is arranged with one end thereof being in contact with the base member fixed to the body and the other end being in contact with a support member of the sensor unit, wherein the spring is configured to generate the urging force in accordance with the distance along the axis from one end, which is in contact with the base member, to the other end, and wherein the mounting unit mounts the flow passage unit on the pressure detection unit in a state where the pressure detecting surface is in contact with the pressure transmitting surface under urging force generated by the urging unit. a pressure detection unit configured to detect a pressure transmitted to a pressure detecting surface; a flow passage unit in which a flow passage configured to cause a fluid to flow in a flow direction from an inflow port to an outflow port and a pressure transmitting surface used for transmitting, to the pressure detecting surface, a pressure of a fluid flowing through the flow passage are formed; and a mounting unit used for removably mounting the flow passage unit on the pressure detection unit, wherein the pressure detection unit includes a body, a sensor unit having the pressure detecting surface, characterized in that the pressure detection device further comprises: a holding unit configured to hold the sensor unit movably along an axis orthogonal to the pressure detecting surface, and an urging unit configured to generate urging force to urge the sensor unit toward the pressure transmitting surface, the urging unit comprising a spring and a base member, wherein the spring is arranged with one end thereof being in contact with the base member fixed to the body and the other end being in contact with a support member of the sensor unit, wherein the spring is configured to generate the urging force in accordance with the distance along the axis from one end, which is in contact with the base member, to the other end, and wherein the mounting unit mounts the flow passage unit on the pressure detection unit in a state where the pressure detecting surface is in contact with the pressure transmitting surface under urging force generated by the urging unit. a body, a sensor unit having the pressure detecting surface, characterized in that the pressure detection device further comprises: a holding unit configured to hold the sensor unit movably along an axis orthogonal to the pressure detecting surface, and an urging unit configured to generate urging force to urge the sensor unit toward the pressure transmitting surface, the urging unit comprising a spring and a base member, wherein the spring is arranged with one end thereof being in contact with the base member fixed to the body and the other end being in contact with a support member of the sensor unit, wherein the spring is configured to generate the urging force in accordance with the distance along the axis from one end, which is in contact with the base member, to the other end, and wherein the mounting unit mounts the flow passage unit on the pressure detection unit in a state where the pressure detecting surface is in contact with the pressure transmitting surface under urging force generated by the urging unit. a holding unit configured to hold the sensor unit movably along an axis orthogonal to the pressure detecting surface, and an urging unit configured to generate urging force to urge the sensor unit toward the pressure transmitting surface, the urging unit comprising a spring and a base member, wherein the spring is arranged with one end thereof being in contact with the base member fixed to the body and the other end being in contact with a support member of the sensor unit, wherein the spring is configured to generate the urging force in accordance with the distance along the axis from one end, which is in contact with the base member, to the other end, and wherein the mounting unit mounts the flow passage unit on the pressure detection unit in a state where the pressure detecting surface is in contact with the pressure transmitting surface under urging force generated by the urging unit.