The invention provides an overload detector with a simplified system configuration to be applied to a railway car having a connecting bogie. A connecting bogie 52 (two axle bogie) having front and rear wheels 52C and 52D are disposed to extend between a first car C.sub.1 and a second car C.sub.2. The front and rear cars C.sub.1 and C.sub.2 are supported via air springs 52A and 52B on the connecting bogie 52. The other end of the car C.sub.1 is supported via air springs 51A and 51B on a bogie 51 (two axle bogie) having front and rear wheels 51C and 51D. The other end of the car C.sub.2 is supported via air springs 53A and 53B on a bogie 53 (two axle bogie) having front and rear wheels 53C and 53D. Pneumoelectric converters 41 and 42 are disposed along paths of pneumatic pipings 21 and 22, and the inner pressure of air springs 51A and 51B is converted into an inner pressure signal AS1, and the inner pressure P.sub.AS2 of the air springs 52A and 52B is converted into an inner pressure signal AS2. The inner pressure signals AS1 and AS2 output from the pneumoelectric converters 41 and 42 are input to a computing processor 3. Overload is determined based on signals AS1 and AS2.