A hydraulic motor 10 of the invention includes a detected unit 52 formed on an outer circumferential surface of a cylinder block 14 and a rotation sensor 50arranged opposed to the detected unit 52 for detecting the detected unit 52. The rotation sensor 50 is provided on a position corresponding to a position between a deepest portion 41 of a cylinder hole 29 and a rear end face 28 of the cylinder block in an axial direction of the cylinder block. A fan driving device 60 is provided with the hydraulic motor 10, a bracket 61 to which the hydraulic motor is attached in a state in which a tip end of the rotational shaft 13 is arranged on a surface side thereof through a through-hole 64 and a fan 62 attached to the rotational shaft 13 and is driven by the hydraulic motor.