A normally open valve unit to close a channel, a microfluidic device equipped with the same, and a method of driving the valve unit are provided. The valve unit includes a valve substance including a phase transition material, a valve substance chamber which communicates with the channel and in which the valve substance is disposed, and a fusion structure formed in a section of the channel in which, wherein when the valve substance contained in the valve substance chamber is fused by applied energy and flows into the section of the channel in which the fusion structure is formed, and the valve substance is heated to melt the fusion structure and conduct fused bonding of the channel, thereby closing the channel.