To solve the problem that a known structure of an inkjet droplet generator may cause a difficulty in adjusting the droplet speed and/or the droplet weight.

The droplet injection device has the droplet generator and a droplet injection waveform to be impressed to the droplet generator during a droplet injection cycle period. The droplet injection waveform includes a first polar pulse, a first second-polar pulse, a delaying period, and a second second-polar pulse in turn.