A multi-mode temperature measuring device, comprising: a first case having a measuring portion and a bottom portion, wherein the measuring portion and the bottom portion are located at opposite sides of the first case, and the measuring portion has a first through hole; characterized by: a second case connected with the first case and being rotatable from a first position to a second position with respect to the first case, the second case having a top portion; an infrared sensing element disposed at the measuring portion and corresponding to the first through hole; and a wave-collection element disposed in the top portion of the second case and having a second through hole, the wave-collection element being configured to collect IR radiation through the second through hole; wherein, when the second case is located at the first position, the second through hole is disposed corresponding to the first through hole, and the top portion covers the measuring portion so that IR radiation is collected by the wave-collection element through the second through hole and further received by the IR sensing element through the first through hole, in order to operate at a forehead-temperature measuring mode, and when the second case is located at the second position, the second case is fixed at the bottom portion of the first case, in order to operate at an ear-temperature measuring mode. a first case having a measuring portion and a bottom portion, wherein the measuring portion and the bottom portion are located at opposite sides of the first case, and the measuring portion has a first through hole; characterized by: a second case connected with the first case and being rotatable from a first position to a second position with respect to the first case, the second case having a top portion; an infrared sensing element disposed at the measuring portion and corresponding to the first through hole; and a wave-collection element disposed in the top portion of the second case and having a second through hole, the wave-collection element being configured to collect IR radiation through the second through hole; wherein, when the second case is located at the first position, the second through hole is disposed corresponding to the first through hole, and the top portion covers the measuring portion so that IR radiation is collected by the wave-collection element through the second through hole and further received by the IR sensing element through the first through hole, in order to operate at a forehead-temperature measuring mode, and when the second case is located at the second position, the second case is fixed at the bottom portion of the first case, in order to operate at an ear-temperature measuring mode. a second case connected with the first case and being rotatable from a first position to a second position with respect to the first case, the second case having a top portion; an infrared sensing element disposed at the measuring portion and corresponding to the first through hole; and a wave-collection element disposed in the top portion of the second case and having a second through hole, the wave-collection element being configured to collect IR radiation through the second through hole; wherein, when the second case is located at the first position, the second through hole is disposed corresponding to the first through hole, and the top portion covers the measuring portion so that IR radiation is collected by the wave-collection element through the second through hole and further received by the IR sensing element through the first through hole, in order to operate at a forehead-temperature measuring mode, and when the second case is located at the second position, the second case is fixed at the bottom portion of the first case, in order to operate at an ear-temperature measuring mode.