Calibration of an up-down type Mach probe is performed using a fast-flowing plasma produced by a magneto-plasma-dynamic arcjet. Mach probe data are compared with ion acoustic Mach numbers Mi, which are calculated using a plasma flow velocity Up and an ion temperature Ti measured by spectroscopy and electron temperature Te by Langmuir probe. The obtained data are also compared with Hutchinson's PIC simulation results in an unmagnetized plasma and are in good agreement with each other. First attempts to measure plasma flow field using a Mach probe are performed at the open-end section in GAMMA10. It is found that Mi at r=0 is more than 2, namely a supersonic plasma flow is formed in the end-cell region.