US Patent 7523659 Flow measurement apparatus

In a thermal type flow rate measurement apparatus comprising a sub-passage having a detour passage and a hole just before a flow rate measuring part, for preventing its output value from falling onto a negative side when the flow rate is abruptly changed, a slit is formed downstream of a flow rate detecting element located after the detour passage. The slit hole may be arranged between the flow rate detecting element and the outlet port part, and may be opened between a wall surface side and a recess part. Thereby, it is possible to prevent the output value from falling in the negative side upon rise-up thereof.