A scanning tunnel microscope is arranged by a combination of an optical microscope and a tunnel scanning unit. The scanning tunnel unit includes a probe held to be spaced apart from a sample placed on a sample table by a predetermined interval in an axial direction, and an actuator for axially moving the sample table and the probe to a tunnel region and relatively and three-dimensionally driving the sample table and the probe. An objective lens and the probe are arranged such that the axis of the probe of the scanning tunnel unit is aligned with an optical axis of the objective lens of the optical microscope. The sample and the probe are axially moved and brought into the tunnel region, and the sample is scanned in its surface direction while the sample and the probe are finely moved in the axial direction and a tunnel current is kept constant, thereby performing an STM observation of an observation surface of the sample. The objective lens of the optical microscope is axially moved to obtain an in-focus state, and the field of the STM observation surface is observed as an optical microscopic image through an eyepiece lens.