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 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 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.