An ECU as a valve body operation estimation device includes a sampling unit that obtains at least one of voltage and current of the electromagnetic coil as sample values at intervals of a predetermined time in a sampling period set based on a predetermined reference timing, a variation calculation unit that calculates a degree of variation of the sample values obtained in the sampling period, a variation waveform which represents a change of the degree of variation caused by shifting the reference timing including a point at which the degree of variation reduces and then rises as the reference timing is delayed, the point referred to as a rising start point, and a timing estimation unit that estimates an operation timing of a valve body based on the reference timing at the rising start point.