The effect of a change in the consumer's income on his total satisfaction is known as income effect. A consumer will be more or less satisfied when his income increases or decreases, keeping the price of goods he buys as constant.

The income effect may be defined, 

as the effect on the purchases of the consumer caused by changes in income with prices of goods remaining constant.

The consumer is in equilibrium at points Q, Q', Q'', Q'''  where his income increase but the prices of the commodities remain the same.

With the increase in income there is a parallel shift upwards in the income line. The new price line are shown as AB, A'B', A''B''......... respectively. Initially the consumer was in equilibrium at point Q, but with increase in income , the equilibrium points move upwards respectively. When all these equilibrium points are joined, we get the Income- Consumption Curve ( ICC) .