A plate-like flow sensor is located in a bypass passage such that a front-to-rear direction of the flow sensor is substantially along a width direction of the bypass passage. The flow sensor divides a flow from its upstream into a first flow, which passes on its front side, and a second flow, which passes on its rear side. The bypass passage has a bent portion in which the first flow and the second flow merge on a downstream side of the flow sensor. A flow deflection unit changes a turning quantity of at least one of the first flow and the second flow such that a turning quantity of the first flow and a turning quantity of the second flow are substantially conformed in the bent portion.