A solid state imaging device and a signal processing method therefor as well as a camera by which a reference signal for cancellation of vertical string-like fixed pattern noises can be obtained readily. In an initial stage after a power supply to the device is made available, a substrate pulse is outputted from a timing generator to reset pixel transistors immediately before pixel signals are read out. Then, in a condition wherein there is no signal originating from incidence of light, an operation pulse signal is caused to rise immediately to read out pixel signals from the pixel transistors through operation switches so as to be held by capacitors. Thereafter, in a horizontal image period, a horizontal scanning pulse signal is outputted from a horizontal shift register to successively put horizontal switches into a connecting state to successively output the signals of the capacitors thereby to obtain a reference signal for cancellation of vertical string-like fixed pattern noises.