The present invention describes a measuring device for a flame, in particular for use in a regulating device for a burner (13), comprising an ionization electrode (15) which is arranged in the flame region (14) of the burner (13) and to which an ac voltage is applied whereby a dc voltage component is superimposed in dependence on the ionization current. The flame resistance influences the ac voltage and the dc voltage at a blocking capacitor (3) unequally. The ac voltage can be separated from the dc voltage component by way of first means (5, 6) and the separated ac voltage can be compared to the separated-off dc voltage component by way of second means (9, 10) in order to produce a pulse width-modulated signal.