Provided is a microfluidic device and microfluidic system with the device. The microfluidic device includes a substrate; a channel formed in the substrate and in which a fluid can move; a valve controlling flow of a fluid flowing along the channel and including a phase transition material which can be melted by energy such as electromagnetic wave energy; and a lens disposed on the substrate and adjusting an irradiating region of the valve, onto which the energy is applied.