A data transfer circuit includes at least one data transfer line that transfers digital data, at least one data detecting circuit connected to the transfer line, holding circuits that hold digital values corresponding to input levels and that transfer the digital values to the transfer line, a scanning circuit that selects a holding circuit, at least one test-pattern generating circuit that generates a digital value, the test-pattern generating circuit connected to the transfer line, at least one test-column scanning circuit that selects the test-pattern generating circuit, and a start-pulse selecting circuit that controls starting of the scanning circuit and the test-column scanning circuit. The start-pulse selecting circuit transfers a digital value to the data transfer line by activating the test-pattern generating circuit.