A polarization tracking device adapted to track polarization fluctuation of a light wave transmitted through an optical fiber using a Stokes vector, comprising: vector calculating means for calculating the Stokes vector of the light wave; rotation angle updating means for expressing a fluctuation amount of the Stokes vector on a Poincare sphere in an xy plane perpendicular to a travelling direction of the light wave using a first angle and a second angle, the first angle being an angle between a direction of an optical electric field of the light wave and a y axis, and the second angle being a phase difference between a component of the optical electric field in a direction of the y axis and a component of the optical electric field in a direction of an x axis orthogonal to the y axis, wherein the fluctuation amount is expressed by a polarization rotation matrix; and inverse rotation application means for rotating the Stokes vector using an inverse polarization rotation matrix that is an inverse matrix of the polarization rotation matrix; wherein the rotation angle updating means is adapted to update the first angle and the second angle based on an S1 parameter, an S2 parameter and an S3 parameter of the Stokes vector, wherein, with respect to an optical modulation signal that is modulated using a phase modulation scheme, the rotation angle updating means is adapted to calculate θ and φ using a formula , where S0, S1, S2, and S3 defined by a formula represent Stokes parameters, X represents the component of the optical electric field in the direction of the x axis, and Y represents the component of the optical electric field in the direction of the y axis, θ (0 ≤ θ ≤ π) represents the first angle, φ (-π/2 ≤ φ ≤ π/2) represents the second angle, and μ represents a step size parameter that determines a tracking speed and tracking accuracy [Formula 1] S 0 S 1 S 2 S 3 = X 2 + Y 2 X 2 − Y 2 2 Re X ⋅ Y ∗ 2 Im X ⋅ Y ∗ [Formula 2] φ k + 1 = φ k − μ sin θS 1 sin φS 2 + cos φS 3 θ k + 1 = θ k − μ S 1 − sin θS 1 − cos θ cos φ S 2 + cos θ sin φS 3 vector calculating means for calculating the Stokes vector of the light wave; rotation angle updating means for expressing a fluctuation amount of the Stokes vector on a Poincare sphere in an xy plane perpendicular to a travelling direction of the light wave using a first angle and a second angle, the first angle being an angle between a direction of an optical electric field of the light wave and a y axis, and the second angle being a phase difference between a component of the optical electric field in a direction of the y axis and a component of the optical electric field in a direction of an x axis orthogonal to the y axis, wherein the fluctuation amount is expressed by a polarization rotation matrix; and inverse rotation application means for rotating the Stokes vector using an inverse polarization rotation matrix that is an inverse matrix of the polarization rotation matrix; wherein the rotation angle updating means is adapted to update the first angle and the second angle based on an S1 parameter, an S2 parameter and an S3 parameter of the Stokes vector, wherein, with respect to an optical modulation signal that is modulated using a phase modulation scheme, the rotation angle updating means is adapted to calculate θ and φ using a formula , where S0, S1, S2, and S3 defined by a formula represent Stokes parameters, X represents the component of the optical electric field in the direction of the x axis, and Y represents the component of the optical electric field in the direction of the y axis, θ (0 ≤ θ ≤ π) represents the first angle, φ (-π/2 ≤ φ ≤ π/2) represents the second angle, and μ represents a step size parameter that determines a tracking speed and tracking accuracy [Formula 1] S 0 S 1 S 2 S 3 = X 2 + Y 2 X 2 − Y 2 2 Re X ⋅ Y ∗ 2 Im X ⋅ Y ∗ [Formula 2] φ k + 1 = φ k − μ sin θS 1 sin φS 2 + cos φS 3 θ k + 1 = θ k − μ S 1 − sin θS 1 − cos θ cos φ S 2 + cos θ sin φS 3 <EOS>