PURPOSE: To make exact measurement without the effect of gas apparatus possible by providing inside of outlet with a throttle plate, a perforated plate with panching medal or sintered metal or a buffer flowpath.

CONSTITUTION: In the outlet 3 of an exclusive gas meter 1 for example, a buffer flowpath 5 is formed by arranging abstraction plates 6 by turns. A gas engine heat pump (GHP) 7 is usually provided with zero-governer 8 in the front to make gas intake constant, and so a large pressure loss at the exclusive gas meter 1 does not matter. In the case of CHP 7, by setting an exclusive gas meter 1, the fluctuation of gas pressure generated by the GHP 7 is not transmitted to the original meter 9 side and thus, exact measurement is done with the original meter 9. Also the fluctuation of gas pressure generated by the GHP 7 is not transmitted to other gas apparatus through branch gas supply lines 11, and so the effect to other gas apparatus such as obstruction of normal burning can be eliminated.