To provide a trace sample measuring device for quantitatively measuring a trace sample by a simple operation without requiring any complicated device or control.

This trace sample measuring device is made up of a first flow path comprising a sample inflow port and a transfer control means, a second flow path comprising a sample outflow port and a transfer control means, and a flow path for measurement comprising an inflow port for a sample transfer fluid and a sensor part for detecting a fluid sample in the flow paths. This device is capable of: (A) causing the fluid sample to flow in from the inflow port, causing the fluid sample to flow into the flow path for measurement from the first flow path, and then stopping the inflow of the fluid sample into the second flow path; (B) stopping the inflow of the fluid sample by the detection of the sensor part at a time point when the fluid sample flowing into the flow path for measurement reaches a designated amount; (C) transferring the fluid sample into the flow path for measurement to the second flow path by means of the transfer fluid, the sample measured is cause to flow out of the outflow port, then bringing the inside of the second flow path to a liquid feedable state, and preventing the fluid sample from flowing into the first flow path.