An air flow rate measurement device includes a housing that includes a bypass flow channel, which branches from a main flow channel and then returns to the main flow channel, a flow rate sensor assy that incorporates a flow rate sensor element, which measures a flow rate of air flowing through the bypass flow channel, and a physical quantity sensor assy that incorporates a physical quantity sensor element, which measures a physical quantity of air flowing through the main flow channel. The housing includes a first mount part on which the flow rate sensor assy is mounted, and a second mount part on which the physical quantity sensor assy is mounted. The flow rate sensor assy and the physical quantity sensor assy are attached to the housing from the same direction to be mounted on the first mount part and the second mount part respectively.