The solenoids used in the RoboCup soccer middle-sized league are large-diameter push solenoids, which are not widely available in the market as a product. Therefore, the relationship between input and output can only be obtained through experiments by researchers who have manufactured the solenoids. Until now, simulations have been performed using FEM and other methods, but it was not possible to analyze the actual plunger motion. In this study, the motion of a plunger is observed using an actual solenoid, and the input-output relationship is clarified. This will allow us to clarify the equation relating ball flight distance and self-inductance as an actual ball ejection device. This research can be utilized not only for Robocup but also for the injection mechanism of Elide Fire Ball and inexpensive and compact ball ejector.