A vehicle weight measurement device provided at a suspension device and comprising: a mounting part of which an upper surface-side is fixed to a vehicle-side and a lower surface-side is provided with a groove portion opening in an annular shape, an annular diaphragm configured to cover an opening area of the groove portion and to form an oil chamber of a predetermined space together with the groove portion, an annular inner collar configured to sandwich and hermetically fix a surface part near an inner diameter of the diaphragm between the inner collar and an inner surface part of the opening area of the groove portion, an annular outer collar having a diameter greater than an outer diameter of the opening area of the groove portion and configured to sandwich and hermetically fix a surface part near an outer diameter of the diaphragm between the outer collar and an outer surface part of the opening area of the groove portion, a piston provided to be moveable in a longitudinal direction of the suspension device between an outer diameter of the inner collar and an inner diameter of the outer collar and configured to press the diaphragm by a resilient force of a spring of the suspension device, a bush configured to receive one end of the spring, and a bearing device interposed between the piston and the bush and configured to be relatively rotatable, wherein the oil chamber is filled with a predetermined fluid to be measured and a pressure of the fluid to be measured, which is to be applied by movement of the piston, is changeable, and wherein the vehicle weight measurement device comprises a pressure sensor configured to communicate with the oil chamber and to detect a change in pressure of the fluid to be measured filled in the oil chamber, characterized in that the bearing device is a thrust angular ball bearing interposed between the piston and the bush and configured to be relatively rotatable, wherein a contact surface between the piston and the diaphragm is arranged so that an extension line in a contact angle direction of the thrust angular ball bearing passes therethrough. a mounting part of which an upper surface-side is fixed to a vehicle-side and a lower surface-side is provided with a groove portion opening in an annular shape, an annular diaphragm configured to cover an opening area of the groove portion and to form an oil chamber of a predetermined space together with the groove portion, an annular inner collar configured to sandwich and hermetically fix a surface part near an inner diameter of the diaphragm between the inner collar and an inner surface part of the opening area of the groove portion, an annular outer collar having a diameter greater than an outer diameter of the opening area of the groove portion and configured to sandwich and hermetically fix a surface part near an outer diameter of the diaphragm between the outer collar and an outer surface part of the opening area of the groove portion, a piston provided to be moveable in a longitudinal direction of the suspension device between an outer diameter of the inner collar and an inner diameter of the outer collar and configured to press the diaphragm by a resilient force of a spring of the suspension device, a bush configured to receive one end of the spring, and a bearing device interposed between the piston and the bush and configured to be relatively rotatable, wherein the oil chamber is filled with a predetermined fluid to be measured and a pressure of the fluid to be measured, which is to be applied by movement of the piston, is changeable, and wherein the vehicle weight measurement device comprises a pressure sensor configured to communicate with the oil chamber and to detect a change in pressure of the fluid to be measured filled in the oil chamber, characterized in that the bearing device is a thrust angular ball bearing interposed between the piston and the bush and configured to be relatively rotatable, wherein a contact surface between the piston and the diaphragm is arranged so that an extension line in a contact angle direction of the thrust angular ball bearing passes therethrough.