To realize a multi-gradation expression without reducing a printing speed.

This liquid droplet discharge controlling device compares printing data SI of which the printing is performed at n+1th time with printing data of which the printing is performed at nth time for each pixel information corresponding to the same nozzle, regarding the printing data SI comprising pixel information of a specified quantity. Then, the liquid droplet discharge controlling device converts the printing data SI into differential data comprising a data variation nozzle SN indicating the presence/absence of a variation, and variation data SND comprising pixel information corresponding to a nozzle having a variation (S1 to S3). When a maximum data amount of the differential data corresponding to each printing data SI is smaller than the data amount of the printing data SI, a conversion data signal SLb comprising the differential data is output (steps S4 to S8). In a data updating section 230 to which the conversion data signal SLb is input, the printing data SI at nth time which is stored in advance is updated from the conversion data signal SLb, and is restored to the printing data SI at n+1th time.

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