The difference between absolute monarchy and constitutional monarchy lies on the fact that in the absolute monarchy, the monarch holds the supreme or absolute powers, whereas in the constitutional monarchy, the head of state is a hereditary or elected monarch. In a constitutional monarchy, the power of the head is limited or boundary by the legislation outlined in a constitution
The law within a constitutional monarchy may differ from the law within an absolute monarchy. Differences between absolute and constitutional monarchies arised during the sixteenth and seventeenth centuries
Absolute monarchy is also known as undemocratic monarchy and constitutional monarchy is also denominateda liberal monarchy.
To sum up, the great main difference is that in the constitutional monarchy, the power of the monarch, who is the head, is lmited by the constitution.