An operation control device of a reciprocating compressor, comprising: a power supply unit configured to supply an AC power of a predetermined frequency; a reciprocating compressor having a predetermined inductance; a capacitor electrically connected to a motor of the reciprocating compressor and having a predetermined capacitance; a control unit (Tr) connected in series to the motor of the reciprocating compressor and configured to apply the AC power to the motor of the reciprocating compressor according to a control signal; a current detector configured to detect a current applied to the motor of the reciprocating compressor; a voltage detector configured to detect a voltage applied to the motor of the reciprocating compressor; a stroke estimator configured to estimate a stroke by calculating the current and voltage applied to the motor of the reciprocating compressor; and a controller configured to detect a load variation amount on the basis of a phase difference between the estimated stroke and the current applied to the motor and configured to control on and off of the control unit (Tr) according to the detected load variation amount, characterized in that the device further comprises a switch unit configured to be switched by the control signal of the controller and to selectively connect a front end of the control unit (Tr) to the power supply unit such that the AC power applied to the motor is passed through the control unit (Tr) or to selectively connect a rear end of the control unit (Tr) to the power supply unit such that a current path to the control unit (Tr) is cut off, wherein if the detected load variation amount is smaller than a preset reference load variation amount, the controller is configured to apply the AC power to the motor by cutting off the current path to the control unit (Tr) by turning on the switch unit such that the rear end of the control unit (Tr) is connected to the power supply unit, and wherein if the detected load variation amount is larger than the preset reference load variation amount, the controller is configured to vary the AC power applied to the motor of the reciprocating compressor by turning on and off the control unit (Tr). a power supply unit configured to supply an AC power of a predetermined frequency; a reciprocating compressor having a predetermined inductance; a capacitor electrically connected to a motor of the reciprocating compressor and having a predetermined capacitance; a control unit (Tr) connected in series to the motor of the reciprocating compressor and configured to apply the AC power to the motor of the reciprocating compressor according to a control signal; a current detector configured to detect a current applied to the motor of the reciprocating compressor; a voltage detector configured to detect a voltage applied to the motor of the reciprocating compressor; a stroke estimator configured to estimate a stroke by calculating the current and voltage applied to the motor of the reciprocating compressor; and a controller configured to detect a load variation amount on the basis of a phase difference between the estimated stroke and the current applied to the motor and configured to control on and off of the control unit (Tr) according to the detected load variation amount, characterized in that the device further comprises a switch unit configured to be switched by the control signal of the controller and to selectively connect a front end of the control unit (Tr) to the power supply unit such that the AC power applied to the motor is passed through the control unit (Tr) or to selectively connect a rear end of the control unit (Tr) to the power supply unit such that a current path to the control unit (Tr) is cut off, wherein if the detected load variation amount is smaller than a preset reference load variation amount, the controller is configured to apply the AC power to the motor by cutting off the current path to the control unit (Tr) by turning on the switch unit such that the rear end of the control unit (Tr) is connected to the power supply unit, and wherein if the detected load variation amount is larger than the preset reference load variation amount, the controller is configured to vary the AC power applied to the motor of the reciprocating compressor by turning on and off the control unit (Tr).