An insulation test apparatus and method for a circuit board having a plurality of wiring patterns formed thereon includes: selection means for selecting wiring patterns to be tested, power supply means for sending a predetermined electrical output between a first object to be measured and a target object to be measured; measurement means for measuring an electrical signal between the first object to be measured and the target object to be measured; and calculation means for calculating the resistance of an insulation failure portion between the first object to be measured and the target object to be measured.