A seat device comprising: a cushion pad; and a plurality of pressure sensitive switches (SW1, SW2, SW3, SW4) configured to detect a load applied from a seating face of the cushion pad, wherein: a lower face of the cushion pad is formed with a groove (50, 51, 52) for concentrating pressing force that collects a pressure applied to the cushion pad; the pressure sensitive switches are disposed in a space of the groove; and in the groove (50, 51, 52), when a width of the groove (50, 51, 52) in a direction the same as a direction orthogonal to a longitudinal direction of the cushion pad is defined as one, a ratio of a length of the groove (50, 51, 52) in a direction the same as the longitudinal direction of the cushion pad is defined as two or greater, and a pressure propagates through the length direction of the groove (50, 51, 52) and acts on the pressure sensitive switches (SW1, SW2, SW3, SW4); wherein the groove (50, 51, 52) is disposed in a region located on the inner side with respect to the peripheral portion of the bottom face of the cushion pad; wherein a gap is formed between the groove (50, 51, 52) and the pressure sensitive switches (SW1, SW2, SW3, SW4); the seat device being characterized in that the gap is continuously formed in a same thickness from one of the pressure sensitive switches (SW1, SW3) to another one of the pressure sensitive switches (SW2, SW4). a cushion pad; and a plurality of pressure sensitive switches (SW1, SW2, SW3, SW4) configured to detect a load applied from a seating face of the cushion pad, wherein: a lower face of the cushion pad is formed with a groove (50, 51, 52) for concentrating pressing force that collects a pressure applied to the cushion pad; the pressure sensitive switches are disposed in a space of the groove; and in the groove (50, 51, 52), when a width of the groove (50, 51, 52) in a direction the same as a direction orthogonal to a longitudinal direction of the cushion pad is defined as one, a ratio of a length of the groove (50, 51, 52) in a direction the same as the longitudinal direction of the cushion pad is defined as two or greater, and a pressure propagates through the length direction of the groove (50, 51, 52) and acts on the pressure sensitive switches (SW1, SW2, SW3, SW4); wherein the groove (50, 51, 52) is disposed in a region located on the inner side with respect to the peripheral portion of the bottom face of the cushion pad; wherein a gap is formed between the groove (50, 51, 52) and the pressure sensitive switches (SW1, SW2, SW3, SW4); the seat device being characterized in that the gap is continuously formed in a same thickness from one of the pressure sensitive switches (SW1, SW3) to another one of the pressure sensitive switches (SW2, SW4). a lower face of the cushion pad is formed with a groove (50, 51, 52) for concentrating pressing force that collects a pressure applied to the cushion pad; the pressure sensitive switches are disposed in a space of the groove; and in the groove (50, 51, 52), when a width of the groove (50, 51, 52) in a direction the same as a direction orthogonal to a longitudinal direction of the cushion pad is defined as one, a ratio of a length of the groove (50, 51, 52) in a direction the same as the longitudinal direction of the cushion pad is defined as two or greater, and a pressure propagates through the length direction of the groove (50, 51, 52) and acts on the pressure sensitive switches (SW1, SW2, SW3, SW4); wherein the groove (50, 51, 52) is disposed in a region located on the inner side with respect to the peripheral portion of the bottom face of the cushion pad; wherein a gap is formed between the groove (50, 51, 52) and the pressure sensitive switches (SW1, SW2, SW3, SW4); the seat device being characterized in that the gap is continuously formed in a same thickness from one of the pressure sensitive switches (SW1, SW3) to another one of the pressure sensitive switches (SW2, SW4).