A seat condition detection device has a sensor unit including pressure-sensitive switch units that are connected in parallel to each other. Each pressure-sensitive switch unit is switched to an on state or an off state depending on pressure. The pressure-sensitive switch units are scatteredly distributed in a seat. The seat condition detection device determines a load applied on the seat based on an on/off state of the pressure-sensitive switch units. Each pressure-sensitive switch unit includes pressure-sensitive switches that are connected in series to each other. Accordingly, reliability in determination of a load acting on the seat exceeding a predetermined value is enhanced.