To provide a viewfinder to effectively improve operability and visibility of a video image, to provide a method of controlling the viewfinder, and to provide an imaging apparatus.

When a detection signal S0 is off, more specifically, an eye-piece unit 36 is not attached, a CPU 104 supplies a control signal to a first signal processing section 118 to disable video inversion processing, controls a backlight drive section 128 based on second luminance stored in an EEPROM 106, and controls an LED driver 110 based on fourth luminance stored in the EEPROM 106, thus setting the luminance of the video image displayed on a display surface 3402 to have the second luminance, and setting the luminance of first to eighth lamps 120A-120H to the fourth luminance for operation.