Bidirectional recording is carried out with a printer that enables variable size dots of different ink quantities to be created with different driving waveforms W1 and W2. Variables are set to a time delay n0 before output of the driving waveform W1 and a time interval n6 between the driving waveform W1 and the driving waveform W2. The output timings n0 and n6 of the driving waveforms W1 and W2 in the course of a backward pass of main scan are individually regulated on the basis of dots created in a forward pass of the main scan as a reference. This arrangement desirably reduces a positional misalignment of dots created in the forward pass with dots created in the backward pass with regard to each of the variable size dots having different ink quantities, thus ensuring high-quality printing.