A flow rate adjusting device comprising: an ultrasonic flow metering portion configured to measure a propagation time difference between ultrasonic waves transmitted by a pair of oscillators (11, 12) disposed at an upstream side and a downstream side of a straight tube-shaped measurement flow channel to obtain a flow rate of a fluid, the fluid flowing from an inflow port and being circulated through the measurement flow channel; a flow rate adjusting portion configured to adjust the flow rate of the fluid flowing out to an outflow port from the downstream side of the measurement flow channel; a control portion configured to control the flow rate adjusting portion on the basis of the flow rate of the fluid measured by the ultrasonic flow metering portion, the control portion including at least one control board (31, 32); an inflow-side flow channel portion configured to guide the fluid flowing in from the inflow port to the upstream side of the measurement flow channel; and an outflow-side flow channel portion configured to guide the fluid to the outflow port, the fluid flowing out from the downstream side of the measurement flow channel, wherein the flow rate adjusting portion includes a valve body portion and a drive portion configured to cause the valve body portion to advance or recede along a first axis line, the measurement flow channel is disposed along a second axis line parallel to the first axis line, the control board (31, 32) is disposed along a third axis line parallel to each of the first axis line and the second axis line, the flow rate adjusting portion is disposed between the ultrasonic flow metering portion and the control portion in an installation direction orthogonal to an installation surface, characterised in that; the inflow-side flow channel portion includes an inflow-side inclined flow channel inclined in a direction approaching the installation surface from the inflow port to the upstream side of the measurement flow channel, and the outflow-side flow channel portion includes an outflow-side inclined flow channel inclined in a direction approaching the installation surface from the flow rate adjusting portion to the outflow port. an ultrasonic flow metering portion configured to measure a propagation time difference between ultrasonic waves transmitted by a pair of oscillators (11, 12) disposed at an upstream side and a downstream side of a straight tube-shaped measurement flow channel to obtain a flow rate of a fluid, the fluid flowing from an inflow port and being circulated through the measurement flow channel; a flow rate adjusting portion configured to adjust the flow rate of the fluid flowing out to an outflow port from the downstream side of the measurement flow channel; a control portion configured to control the flow rate adjusting portion on the basis of the flow rate of the fluid measured by the ultrasonic flow metering portion, the control portion including at least one control board (31, 32); an inflow-side flow channel portion configured to guide the fluid flowing in from the inflow port to the upstream side of the measurement flow channel; and an outflow-side flow channel portion configured to guide the fluid to the outflow port, the fluid flowing out from the downstream side of the measurement flow channel, wherein