Today's material welfare has been achieved at the expense of consumption of finite resources and generation of environmental burdens. Over the past few decades the volume of global consumption has grown dramatically, while at the same time technological advances have enabled products with greater efficiencies. These two directions of change, consumption growth and technological advance, are the foci of the present paper. Using quantitative measures for these two factors, we define a new indicator, "eco-velocity of consumption", analogous to velocity in physics. The indicator not only identifies the environmental soundness of consumption growth and technological advance but also indicates whether and to what extent our society is shifting toward sustainable consumption. This study demonstrates the practicability of the indicator through a case study in which we calculate the eco-velocities of Japanese household consumption in 2 years: 1995 and 2000. The rate of technological advance during the periods concerned is quantified in terms of the embodied carbon dioxide emission per yen of product. The results show that the current growth rate of Japanese household consumption is greater than the rate of technological advance to mitigate carbon dioxide emissions. The eco-velocities at the level of individual commodity groups are also examined, and the sources of changes in eco-velocity for each commodity are identified using structural decomposition analysis.