A dynamic random access memory device can enter a diagnostic mode of operation to see whether or not undesirable short-circuit takes place in a word line and/or a control signal line for transfer gates between bit lines and a sense amplifier unit, and a built-in testing operation discriminating unit discriminates the testing operation on the word lines and the control signal lines from other testing operations for causing a power supply system to interrupt electric power to a row address decoder unit and a driver unit for the control signal lines so that voltage level on a word line and/or a control signal line is rapidly decayed due to the short-circuit, thereby screening out the defective products before the delivery from the manufacturer.