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 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 , when a width of the groove 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 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 and acts on the pressure sensitive switches (SW1, SW2, SW3, SW4); wherein the groove 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 (GP) is formed between the groove 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 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 , when a width of the groove 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 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 and acts on the pressure sensitive switches (SW1, SW2, SW3, SW4); wherein the groove 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 (GP) is formed between the groove 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 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 , when a width of the groove 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 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 and acts on the pressure sensitive switches (SW1, SW2, SW3, SW4); wherein the groove 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 (GP) is formed between the groove 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). <EOS>