An apparatus for detecting an ovality of a circumference of a cross section of a heat exchanger tube, the apparatus comprising: a probe body configured to be inserted in the heat exchanger tube, moveable in a lengthwise direction of the heat exchanger tube, and rotatable in a circumferential direction of an inner surface of the heat exchanger tube; support foots (122, 132) disposed at both ends of the probe body to support a linear movement and a rotation of the probe body; a coil support unit provided in the probe body; and an eddy current coil mounted on the coil support unit, and including at least a first coil unit and a second coil unit disposed at different locations in a circumferential direction of the probe body and configured to measure an eddy current resistance according to a change in a distance between the inner surface of the heat exchanger tube and said first coil unit and said second coil unit when said probe body is rotating relative to said heat exchanger tube in order to detect the ovality of the heat exchanger tube, wherein the eddy current coil uses one coil unit among the first coil unit and the second coil unit as a test coil and a remaining coil as a reference coil, or uses the first coil unit and the second coil unit as test coils, and wherein the apparatus is configured to detect the ovality of the heat exchanger tube and a degree of the ovality using an amplitude difference between signals measured in the first coil unit and the second coil unit in dependence on a difference between a distance from the first coil unit to the inner surface of the heat exchanger tube and a second distance from the second coil unit to the inner surface of the heat exchanger tube. a probe body configured to be inserted in the heat exchanger tube, moveable in a lengthwise direction of the heat exchanger tube, and rotatable in a circumferential direction of an inner surface of the heat exchanger tube; support foots (122, 132) disposed at both ends of the probe body to support a linear movement and a rotation of the probe body; an eddy current coil mounted on the coil support unit, and including at least a first coil unit and a second coil unit disposed at different locations in a circumferential direction of the probe body and configured to measure an eddy current resistance according to a change in a distance between the inner surface of the heat exchanger tube and said first coil unit and said second coil unit when said probe body is rotating relative to said heat exchanger tube in order to detect the ovality of the heat exchanger tube, wherein the eddy current coil uses one coil unit among the first coil unit and the second coil unit as a test coil and a remaining coil as a reference coil, or uses the first coil unit and the second coil unit as test coils, and wherein the apparatus is configured to detect the ovality of the heat exchanger tube and a degree of the ovality using an amplitude difference between signals measured in the first coil unit and the second coil unit in dependence on a difference between a distance from the first coil unit to the inner surface of the heat exchanger tube and a second distance from the second coil unit to the inner surface of the heat exchanger tube.