A device for measuring resistance of a ground tap and a charger for an on-board vehicle including the device. The device includes a current source and an ammeter disposed on a first electrical branch, provided to link a phase of a power supply network with the ground of the installation; a second electrical branch provided to link a neutral wire of the power supply network with the ground of the installation, including a resistor across terminals of which is connected a voltmeter, and a first capacitor in series with the resistor; and a third electrical branch is provided for linking the neutral wire of the network with the ground of the installation, and including, on the third branch, in parallel with the first capacitor and with the first resistor, a second capacitor of higher value than the first capacitor.