To provide a system wherein a low ink level signal is generated by sensing variation in the weight of an ink reservoir.

An ink reservoir 8 is equipped to a support platform 30 so that the platform 30 supports at least a weight of the ink reservoir. A strain gage 32 or another weight sensor is fitted to the platform 30, and incorporated into a circuit providing a signal output expressing variation in the weight of the platform, i.e., variation in weight of the ink reservoir. The output signal is digitalized to be sent to a controller 20. When it reaches a preliminarily set reference signal level or exceeds that, an output low ink level signal is generated, and a display or an alarm indicating existence of a low ink level state to a user is generated.