To provide a vapor-liquid mixed microflow measuring device for measuring a flow rate highly accurately by detecting an interface domain of fluid in a capillary.

This vapor-liquid mixed microflow measuring device includes a core holder 1 for supplying fluid F by press-fit gas G, a capillary 2 having a smaller diameter than a bubble spherical diameter, a first light emitter 3a and a second light emitter 3b for emitting detection light A in the facing state to the capillary 2, a first light receiver 4a and a second light receiver 4b for receiving transmitted light B, a vapor-liquid interface detection means 5 for detecting the interface domain based on a correlation detected from the transmitted light B, and a flow measuring means 6 for measuring the flow rate based on detection by the vapor-liquid interface detection means 5.