To provide a swash plate inclination angle detection device having high degree of freedom of a mounting position and allowing deviation of a central position.

A swash plate plunger type hydraulic motor M is constituted by fitting and arranging a plunger 33 into a plunger hole of a motor cylinder 32 slidably and supporting a motor swing member 35 having a motor swash plate member 31 so as to incline and swing freely by a motor casing 30. The swash plate inclination angle detection device detecting a swash plate angle is composed of an angle detector 37 attached to a transmission housing HSG and a rotation connection mechanism 40 connecting the motor swing member with the angle detector. This rotation connection mechanism is composed of a first connection rod 41 engaged with the motor swing member on the same shaft as its inclination swing shaft, a second connection rod 42 connected with the angle detector, and a universal joint connecting the first connection rod with the second connection rod.