A signal processing apparatus and a signal processing method that process a signal to control exposure timing of an image sensor, and an imaging device are provided. The signal processing apparatus includes a first adjustment unit that adjusts exposure density in an exposure period, and a second adjustment unit that adjusts a start time and an end time of exposure in a frame period, and provides a control signal to control exposure timing by the exposure density between the start time and the end time, to an image sensor including a mechanism to accumulate photoelectrically converted charge a plurality of times separately and then AD-convert and read out total charge, to allow acquisition of a flicker-free high dynamic range image.