A control apparatus for controlling an LC resonant converter comprising a resonant circuit and a signal generation circuit that includes at least two switching elements, that generates a square-waved voltage signal from an input voltage, and that supplies the voltage signal to the resonant circuit, the control apparatus comprising: a drive control unit configured to drive the switching elements in the signal generation circuit such that a square-waved voltage signal is output from the signal generation circuit, and configured to be capable of executing feedback control for controlling a switching frequency of each of the switching elements in the signal generation circuit using an output voltage of the LC resonant converter, such that an output voltage of the LC resonant converter reaches a target voltage, and of executing open-loop control for obtaining a switching frequency at which an output voltage of the LC resonant converter reaches the target voltage, from one or more pieces of information out of the target voltage, an input voltage and an output current of the LC resonant converter, and the drive control unit being configured to drive the switching element in the signal generation circuit at the obtained switching frequency; and a determination unit configured to determine, based on information regarding an operation state of the LC resonant converter, whether or not the operation state of the LC resonant converter is a first state where a change of a predetermined amount or larger may occur in an output voltage if the feedback control is executed, wherein the drive control unit is configured to execute the feedback control if the determination unit determines that the operation state of the LC resonant converter is not the first state, and the drive control unit is configured execute the open-loop control instead of the feedback control if the determination unit determines that the operation state of the LC resonant converter is the first state. a drive control unit configured to drive the switching elements in the signal generation circuit such that a square-waved voltage signal is output from the signal generation circuit, and configured to be capable of executing feedback control for controlling a switching frequency of each of the switching elements in the signal generation circuit using an output voltage of the LC resonant converter, such that an output voltage of the LC resonant converter reaches a target voltage, and of executing open-loop control for obtaining a switching frequency at which an output voltage of the LC resonant converter reaches the target voltage, from one or more pieces of information out of the target voltage, an input voltage and an output current of the LC resonant converter, and the drive control unit being configured to drive the switching element in the signal generation circuit at the obtained switching frequency; and a determination unit configured to determine, based on information regarding an operation state of the LC resonant converter, whether or not the operation state of the LC resonant converter is a first state where a change of a predetermined amount or larger may occur in an output voltage if the feedback control is executed, wherein the drive control unit is configured to execute the feedback control if the determination unit determines that the operation state of the LC resonant converter is not the first state, and the drive control unit is configured execute the open-loop control instead of the feedback control if the determination unit determines that the operation state of the LC resonant converter is the first state.