A control valve for a variable displacement compressor for varying a discharging capacity of the compressor for compressing refrigerant led into a suction chamber and discharging the compressed refrigerant from a discharge chamber, by regulating a flow rate of the refrigerant led into a crankcase from the discharge chamber, the control valve comprising: a body having a discharge chamber communication port communicating with the discharge chamber, a crankcase communication port communicating with the crankcase, and a valve hole formed in a passage connecting the discharge chamber communication port and the crankcase communication port; a valve element for opening and closing a valve section, the valve element being arranged in such a manner as to move toward and away from the valve hole; a solenoid that generates a solenoidal force with which to drive the valve element in a valve closing direction in accordance with an amount of current supplied thereto, the solenoid being connected to an end of the body; a transmitting rod (34, 68) that transmits the solenoidal force to the valve element, the transmitting rod (34, 68) being slidably supported in a direction of axis line in the body; a spring that applies a biasing force in a valve opening direction to the transmitting rod (34, 68), the spring being placed in a working chamber formed between the body and the solenoid; and a fitting part fitted with an O-ring, the fitting part being formed by an annular groove provided in an outer peripheral surface of a connection part where the body and the solenoid are connected, the O-ring achieving sealing capability when the control valve is mounted through a mounting hole of the compressor, wherein the body includes a partition wall, a guide portion, and a guiding passage, the partition wall dividing an internal space of the body into a valve chamber and the working chamber, the valve chamber being formed between the valve hole and the crankcase communication port, the guide portion protruding from a center of the partition wall into the working chamber, the guiding passage running through the partition wall and the guide portion in the direction of axis line, wherein the valve element is placed in the valve chamber, wherein the transmitting rod (34, 68) is slidably supported in the guiding passage, one end of the transmitting rod (34, 68) being coupled to the valve element in the valve chamber, the other end thereof being coupled to the solenoid, wherein the guide portion has a shape with an outside diameter gradually reduced from a partition wall side toward a solenoid side, wherein the spring has a shape with an outside diameter getting gradually smaller from the body side toward the solenoid side, and wherein the guide portion coaxially extends into the spring, and the transmitting rod (34, 68) coaxially extends through the spring. a body having a discharge chamber communication port communicating with the discharge chamber, a crankcase communication port communicating with the crankcase, and a valve hole formed in a passage connecting the discharge chamber communication port and the crankcase communication port; a valve element for opening and closing a valve section, the valve element being arranged in such a manner as to move toward and away from the valve hole; a solenoid that generates a solenoidal force with which to drive the valve element in a valve closing direction in accordance with an amount of current supplied thereto, the solenoid being connected to an end of the body; a transmitting rod (34, 68) that transmits the solenoidal force to the valve element, the transmitting rod (34, 68) being slidably supported in a direction of axis line in the body; a spring that applies a biasing force in a valve opening direction to the transmitting rod (34, 68), the spring being placed in a working chamber formed between the body and the solenoid; and a fitting part fitted with an O-ring, the fitting part being formed by an annular groove provided in an outer peripheral surface of a connection part where the body and the solenoid are connected, the O-ring achieving sealing capability when the control valve is mounted through a mounting hole of the compressor, wherein the body includes a partition wall, a guide portion, and a guiding passage, the partition wall dividing an internal space of the body into a valve chamber and the working chamber, the valve chamber being formed between the valve hole and the crankcase communication port, the guide portion protruding from a center of the partition wall into the working chamber, the guiding passage running through the partition wall and the guide portion in the direction of axis line, wherein the valve element is placed in the valve chamber, wherein the transmitting rod (34, 68) is slidably supported in the guiding passage, one end of the transmitting rod (34, 68) being coupled to the valve element in the valve chamber, the other end thereof being coupled to the solenoid, wherein the guide portion has a shape with an outside diameter gradually reduced from a partition wall side toward a solenoid side, wherein the spring has a shape with an outside diameter getting gradually smaller from the body side toward the solenoid side, and wherein the guide portion coaxially extends into the spring, and the transmitting rod (34, 68) coaxially extends through the spring.