To provide an electric resistance measuring instrument which is capable of making stable on-site measurement with high accuracy and allows the correlation with the measured value by the conventional JIS(Japanese Industrial Standard) method.

A bag capturing section 10 extracts waste gases to the outside of a flue, captures dust from these waste gases by a bag filter and receives the captured dust in a lower electrode cell. A bulk density regulating section 20 regulates the bulk density of the dust by applying load on the dust on the lower electrode cell captured in the bag capturing section by means of a weight and roller. A parallel flat plate electrode measuring section 30 measures a slight current flowing to the upper electrode by impressing a power source across the dust subjected to the bulk density regulation between an upper electrode and the lower electrode cell, thereby measuring the electric resistance of the dust.