To suppress false detection of an unattended object, regardless of the amount of infrared ray, when switching an infrared light cut filter.

The image pick-up device includes image capturing mode switching means 116 for switching the image capturing mode by inserting and withdrawing an infrared light cut filter 102, reference image storage means 110 for storing the reference image of each image capturing mode, difference detection means 111 for calculating the difference value of luminance between the reference image and an image under capturing, unattended object detection means 109 performing unattended object detection based on the difference value, luminance change calculation means 105 for calculating a luminance change due to insertion and withdrawal of the infrared light cut filter, and gain control means 104 for controlling the gain of an electric signal in the image capturing means. The gain control means adjusts the gain so as to reduce the luminance change thus calculated, when the image capturing mode is switched.