PURPOSE: To measure the durability of a substrate for an ink jet recording head rapidly, easily and accurately at a low cost by measuring the durability in the electrothermal conversion element in a substrate before cutting into chips.

CONSTITUTION: A circuit in the test of a substrate level is constituted of a diode 1, an electrothermal conversion element 2 being an element to be measured, a switch 3 for selecting the electrothermal conversion element, a pulse power supply 4 and an ammeter 5. In a durability test, the electrothermal conversion element 2 performing the test is selected by changing over the switch 3 and the pulse of the condition determined by the pulse power supply 4 is applied. The resistance change rate of the electrothermal conversion element 2 is observed while a flowing current is measured by the ammeter 5. By this constitution, the easiness of deterioration and life of the electrothermal conversion element are estimated. By employing this method, the quality of the electrothermal conversion element can be judged rapidly, easily and accurately and the cost of the durability test can greatly be reduced.