An RF power supply device for supplying RF power to a load involving electrical discharge, comprising, an RF generator circuit configured to generate a variable frequency; a frequency control circuit configured to output a control signal for controlling frequency change in the RF generator circuit; a state-of-reflection detector circuit including, a phase detector circuit configured to detect a phase state of the RF generator circuit and a reflection arithmetic circuit configured to compute a reflection coefficient value and/or a reflection amount at an output end of the RF generator circuit, a control-direction command circuit configured to output a direction command signal for providing a control direction where the frequency increases or decreases in the frequency change, on the basis of the phase state outputted from the phase detector circuit, and, a recontrol circuit configured to output to the frequency control circuit, a recontrol signal for issuing a command to perform the frequency change again, wherein, the frequency control circuit is configured to perform control for the RF generator circuit to generate the variable frequency, the control comprising, a phase control that is configured to control increase or decrease of the frequency in the frequency change at the time of initiating the control, on the basis of the direction command signal outputted from the control-direction command circuit; and reflected power control that configured to control continuing or stopping the frequency change at the time of completing the control, using as a control end condition, the reflection coefficient value and/or the reflection amount outputted from the reflection arithmetic circuit, and that is configured to output a control signal to the RF generator circuit on the basis of the recontrol signal, and the recontrol circuit; is configured to set as a central value, the reflection coefficient value and/or the reflection amount at the frequency determined according to the frequency change, is configured to hold as a threshold range for determining whether or not the recontrol is to be performed, a range of the reflection coefficient and/or a range of the reflection amount, with a certain width above and below the central value, and is configured to output the recontrol signal in at least either one of the case where the reflection coefficient value detected by the reflection arithmetic circuit is out of the range of the reflection coefficient, and the case where the reflection amount detected by the reflection arithmetic circuit is out of the range of the reflection amount. an RF generator circuit configured to generate a variable frequency; a frequency control circuit configured to output a control signal for controlling frequency change in the RF generator circuit; a state-of-reflection detector circuit including, a phase detector circuit configured to detect a phase state of the RF generator circuit and a reflection arithmetic circuit configured to compute a reflection coefficient value and/or a reflection amount at an output end of the RF generator circuit, a control-direction command circuit configured to output a direction command signal for providing a control direction where the frequency increases or decreases in the frequency change, on the basis of the phase state outputted from the phase detector circuit, and, a recontrol circuit configured to output to the frequency control circuit, a recontrol signal for issuing a command to perform the frequency change again, wherein, the frequency control circuit is configured to perform control for the RF generator circuit to generate the variable frequency, the control comprising, a phase control that is configured to control increase or decrease of the frequency in the frequency change at the time of initiating the control, on the basis of the direction command signal outputted from the control-direction command circuit; and reflected power control that configured to control continuing or stopping the frequency change at the time of completing the control, using as a control end condition, the reflection coefficient value and/or the reflection amount outputted from the reflection arithmetic circuit, and that is configured to output a control signal to the RF generator circuit on the basis of the recontrol signal, and the recontrol circuit; is configured to set as a central value, the reflection coefficient value and/or the reflection amount at the frequency determined according to the frequency change, is configured to hold as a threshold range for determining whether or not the recontrol is to be performed, a range of the reflection coefficient and/or a range of the reflection amount, with a certain width above and below the central value, and is configured to output the recontrol signal in at least either one of the case where the reflection coefficient value detected by the reflection arithmetic circuit is out of the range of the reflection coefficient, and the case where the reflection amount detected by the reflection arithmetic circuit is out of the range of the reflection amount.