tion means is z0, the wavelength of the illuminating light is xcex, a maximum value of a diameter of the probe is dmax within a range from a top end of the probe to a distance z0, and the top end diameter of the probe is d0, the diameter of the probe monotonously increases from the top end to the distance z0, and dmaxxe0x00xa0d0(z0+xcex/0)/(xcex/0) is given. Also, to achieve the above objects, according to the present invention, there is provided a probe used for a near-field optical microscope, comprising: a probe body; and an extending part extending in one direction from the probe body, wherein 