PROBLEM TO BE SOLVED: To provide a biological information acquisition device which can maintain comfort for a seated person and which has high detection accuracy of biological information.SOLUTION: In a seat part 22, a first layer 61, a second layer 62 and a third layer 63 are stacked in order inward from the side near a surface of the seat part 22 rigidity of the second layer 62 is higher than that of the third layer 63 and rigidity of the first layer 61 is lower than that of the third layer 63. A pressure-sensitive part 31 has a pressure-sensitive part body 34 that is arranged between the first and second layers 61 and 62.SELECTED DRAWING: Figure 8