Authors investigated an influence of x-ray tube voltage on x-ray quality and dose with using objects of various thickness, and obtained the results as follows: 1. Radiographic effects were influenced by tube voltages and objects. 2. Dose decrement rates hade more influence upon primary-rays than total x-rays at lower tube voltages. 3. The quality of transmitted x-rays was affected by tube voltages and thickness of objects. 4. Scattered-ray contents were proportional to tube voltages with using grid.