A flow rate adjustment apparatus comprising: a flow rate measurement mechanism that can be attached to an installation surface; and a flow rate adjustment mechanism that is separably attached to the flow rate measurement mechanism , wherein the flow rate measurement mechanism includes: a flow rate measurement unit that measures a flow rate of a fluid that flows through a first flow passage ; and a first casing unit that houses the flow rate measurement unit thereinside and can be attached to the installation surface, the flow rate adjustment mechanism includes: a drive unit that moves a valve body part along an axis line intersecting with the installation surface; a control unit that controls the movement of the valve body part by the drive unit ; a valve main body in which a valve chamber that houses the valve body part , a second flow passage that communicates with a valve hole into which the valve body part is inserted, and a third flow passage that is connected to an external flow passage have been formed; and a second casing unit that houses the drive unit and the control unit thereinside and is attached to the valve main body , characterized in that the flow rate adjustment mechanism is attached to the flow rate measurement mechanism in a state where a clearance (CL) communicating with an outside is provided between the first casing unit and the valve main body , and the flow rate measurement unit has a coupling part that couples the second flow passage extending along the axis line to the first flow passage . a flow rate measurement mechanism that can be attached to an installation surface; and a flow rate adjustment mechanism that is separably attached to the flow rate measurement mechanism , wherein the flow rate measurement mechanism includes: a flow rate measurement unit that measures a flow rate of a fluid that flows through a first flow passage ; and a first casing unit that houses the flow rate measurement unit thereinside and can be attached to the installation surface, a flow rate measurement unit that measures a flow rate of a fluid that flows through a first flow passage ; and a first casing unit that houses the flow rate measurement unit thereinside and can be attached to the installation surface, the flow rate adjustment mechanism includes: a drive unit that moves a valve body part along an axis line intersecting with the installation surface; a control unit that controls the movement of the valve body part by the drive unit ; a valve main body in which a valve chamber that houses the valve body part , a second flow passage that communicates with a valve hole into which the valve body part is inserted, and a third flow passage that is connected to an external flow passage have been formed; and a second casing unit that houses the drive unit and the control unit thereinside and is attached to the valve main body , characterized in that a drive unit that moves a valve body part along an axis line intersecting with the installation surface; a control unit that controls the movement of the valve body part by the drive unit ; a valve main body in which a valve chamber that houses the valve body part , a second flow passage that communicates with a valve hole into which the valve body part is inserted, and a third flow passage that is connected to an external flow passage have been formed; and a second casing unit that houses the drive unit and the control unit thereinside and is attached to the valve main body , characterized in that the flow rate adjustment mechanism is attached to the flow rate measurement mechanism in a state where a clearance (CL) communicating with an outside is provided between the first casing unit and the valve main body , and the flow rate measurement unit has a coupling part that couples the second flow passage extending along the axis line to the first flow passage . <EOS>