To achieve accurate biometric authentication while thinning a device.

The biological information acquisition device acquires biological information of a living body region 100 based on the irradiation of light to the living body region 100. The biological information acquisition device comprises a light source for emitting light to irradiate the living body region 100, an imaging element 1 with a plurality of two-dimensionally disposed pixels, and a dimming member 70 disposed on the imaging element 1. The light transmissivity in a first region R80 of the dimming member located close to the light source is lower than the light transmissivity in a second region R90 of the dimming member located relatively apart from the light source compared with the first region R80.