to a focusing state of an image pick up optical system included in the optical system 32 what is shown as u03bc is a signal including focusing information of the image pick up optical system produced from the position detecting sensor and an amount of a deviation in focusing is presumed by an operation circuit 35 then a presumed value u03c5 is sent to system control means 36 the system control means 36 sends a focusing control signal d to focusing control means 38 of the image pick up optical system according to a magnitude of the presumed value of an amount of deviation in focusing and the focusing control means 38 sends a driving signal depending on d to driving means 37 which is to change a focusing state of the image pick up optical image when the system control means 36 gives a focusing initiation signal stt to the timing pulse generation means 34 the timing pulse generation means 34 sends out timing pulses u03c61 to u03c64 rs for driving the differential type position detecting sensor 33 and at the same time sends a light projection control signal u03c6l to the light projection light source 39 to initiate a detection of a focusing state of the image pick up optical system when an output level of the differential type position detecting sensor 33 reaches a certain level a signal f becomes 34 h 34 thus informing the timing pulse generation means 34 that the signal u03bc including a focusing state has been set after that an amount of deviation in focusing is presumed by the operation means 35 out of the signal u03bc and sends a presumed value u03c5 to.