A probe includes an optical system which irradiates a site of a biological tissue and receives light emitted from the site, and an imaging device. The imaging device is disposed ahead of the optical system closer to the end of the probe. The probe rotates the incident direction of the light and the imaging direction of the imaging device around a rotation axis directed to the longitudinal direction of the probe while fixing an angle between the incident direction and the imaging direction. The optical system receives the light from the site which always falls in the field of view of the imaging device, or brought with a time lag into the field of view of the imaging device as a result of rotation, the light being incident in the direction normal to, or inclined away from the rotation axis.
