A probe for a three-dimensional (3D) scanning optical imaging which prevents rotational irregularity, axial runout, friction, rotation transmission delays of a rotational part by reducing occurrences of rotation transmission delays, torque loss, and the like, and can perform scanning of a certain length in an axial direction and obtain a three-dimensional observation image, in a probe for OCT image diagnosis. A fixed side optical fiber that transmits light between a tip side and a rear side of a probe and is non-rotatably disposed, a first optical path conversion means that rotates to emit a light ray in a substantially radial direction, a rotation side optical fiber which is rotated by a motor, and a second optical path conversion means that rotates and emits light toward the first optical path conversion means are collinearly disposed. In this way, it is possible to obtain a high quality 3D observation image.