To surely extract cause of various abnormal ejections such as thickened ink, occurrence of bubbles, adhesion of dust or the like, in a simple circuit structure.

A liquid ejector is equipped with a memory 216 which stores in advance the peak value of the pressure detection signal of a pressure sensor 59 in a normal ejection state, a comparison circuit 232 which compares the peak value stored in the memory 216 in advance with the pressure detection signal obtained from the pressure sensor 59 during a specified abnormal detection interval to extract a first cause of the abnormal ejection, a variable threshold value setting circuit 242 which sets the variable threshold value corresponding to the difference between the peak value stored in the memory 216 in advance and the peak value of the pressure detection signal obtained from the pressure sensor 59 during the abnormal detection interval, a measured pulse generation circuit 244 which compares the variable threshold value with the pressure detection signal obtained from the pressure sensor 59 during the abnormal detection interval to generate a measurement pulse, and a time measurement circuit 246 which measures the time interval of the measurement pulse to extract a second cause of the abnormal ejection.