PURPOSE: To continuously adjust the depth of field to be photographed without altering an outputted video level by adjusting any one of the sensitivity of a pickup means, the light attenuation quantity of a variable density filter and the gain of a signal process part according to F value information from a diaphragm mechanism.

CONSTITUTION: Light beam from an object condensed by a lens 4, after adjusting its light quantity by the diaphragm 5, is formed with an image on a pickup tube 6, where an optical image is converted into an electrical signal and outputted to a signal process part 7 in a poststage. In this case, the sensitivity of the pickup tube 6 is automatically adjusted with the output from a converter 8 so as not to alter the outputted video level by using the information of F value outputted from the diaphragm 5. Namely, any one of the light attenuation quantity of the variable density filter set on the front surface of the pickup tube 6, the sensitivity of the pickup tube 6 and the gain of the signal process part is automatically adjusted. Thus, the depth of the field to be photographed can be continuously controlled with the image level constant even if the F value is altered.