It is an object of the present invention to provide a data signal generating apparatus which is small in size, and can output the serial data in a desired sequence without assuming an indefinite state as well as being capable of dealing with the jitter measurement. In the data signal generating apparatus according to the present invention, synchronization means 25 for synchronizing a data output unit 11 with a multiplexer 13 has a phase comparator 16 for comparing the phase of a data synchronization clock signal outputted from a data output unit 11 in synchronization with the timing to update parallel data, with the phase of a divided clock signal A produced by dividing the frequency of a reference clock signal CK1 by a plural number “m” in the multiplexer 13, the signal A being used for determining the timing to performing parallel-serial conversion, a variable delay device 30 for adding a desired delay to a data request signal A′, the variable delay device 30 being constituted by an orthogonal modulation type delay device, and a control unit 26 for controlling a direct control signal to be inputted into the variable delay device 30 on the basis of a comparing result obtained from the phase comparator 16 to synchronize the timing to have the data output unit 11 update the parallel data with the timing to have the multiplexer 13 perform parallel-serial conversion processing.