In one embodiment, a waveform generating device includes a first DA converter converting input data, a controller outputting a first signal having a command value based on the input data, and a second signal having a command value differing by a constant value from the first signal, a second DA converter converting the first signal, a third DA converter converting the second signal, and a combiner combining the output of the first DA converter, the output of the second DA converter, and the output of the third DA converter. When a value of a predetermined first high-order bit of the input data is inverted, the controller changes the command value of the first signal such that a value of the first high-order bit or a second high-order bit different from the first high-order bit is inverted.