Part of light emitted from a laser light source (11) for detecting displacement of a cantilever (4) is taken by a half mirror (20) and introduced into a photo-detector (21) having a four-divided light receiving surface. If an emitting direction of the emitted light is inclined by a factor such as a change in an ambient temperature, a light spot position moves on the light reception surface of thephoto-detector (21). Therefore, a quantity of the inclination and the inclined direction in the emitting can be recognized from a quantity and direction of the movement. A drive quantity computing unit (22) calculates the drive quantity according to the quantity and direction of the inclination, and causes an actuator (23) to displace the laser light source (11) around a Y-axis and a Z-axis. Thus, the inclination in the emitting direction can be compensated, and erroneous recognition that a specimen surface is uneven can be prevented.