Solid state imaging device and imaging system

A solid state imaging device includes a photoelectric conversion unit that generates a signal based on an incident light by photoelectric conversion; a transfer unit that transfers the signal from the photoelectric conversion unit; a ramp wave generating unit that has an input node where the signal is transferred and that generates a ramp wave whose voltage changes with time at a slope based on a potential of the input node; a detection unit that detects a change in a relationship between the ramp wave and a threshold voltage; a ramp wave reset unit that resets the ramp wave voltage upon detection of a change in the relationship; a control unit that causes the detection unit to repeatedly detect a change in the relationship; and a digital value acquisition unit that acquires a digital value corresponding to the number of repetitions for which a change in the relationship is detected.