A thermal flow meter capable of measuring flow rates of a gas flowing in a forward direction and a backward direction with a high degree of accuracy is provided. A thermal flow meter 300 according to the present invention includes a bypass passage configured to retrieve and flow a measurement target gas 30 received from a main passage 124 and a flow rate measurement circuit 601 configured to measure a flow rate by performing heat transfer with the measurement target gas flowing in the bypass passage. In an outlet port side chamber 4216 provided at an upstream with respect to an outlet port 352 of the bypass passage which is formed to be open in a downstream direction in a flow direction of the measurement target gas, a guide 4217 is provided to oppose the outlet port to change a direction of a flow of the measurement target gas flowing in from the opposite side, and the outlet port and an inflow unit of the outlet port side chamber are arranged to be eccentric when they are seen in a direction along the flow direction of the measurement target gas flowing in the main passage.