A key structure used in a portable electronic device includes a resilient member forming a plurality of conducting films and a column, a dome member forming an arch portion and a peripheral portion, a circuit board forming a plurality of first terminals, second terminals and a third terminal. The dome member is mounted to the circuit board, the peripheral portion electronically connects to the second terminals, the resilient member covers the dome member, the conducting films conductively contact the first terminals. The resilient member is pressed to make the column resist against the arch portion, thereby the first terminals and the second terminals are both conductive, or the first terminals, the second terminals and the third terminal are all conductive.