To provide an antidewing device for a showcase for preventing a dew formation without wasting an excess energy in response to an indoor atmosphere.

The antidewing device for the showcase comprises a plurality of pairs of surface acoustic wave elements (21a/22a to 21n/22n) installed on outer plate surfaces 12, 14 of the showcase to be antidewed, an exciting means 3A for exciting the ones of the plurality of pairs of the elements (21a to 21n) to transmit surface waves 24j, a dew formation detecting means 4 for detecting the presence or absence of the dew formation according to a receiving amplitude of the wave 24j received by the other elements (22a to 22n) installed oppositely, an antidewing heater 53 installed on the outer plate surface 12 to be antidewed, and a controller 5 for controlling the means 3A and the means 4A to supply a heater current 52b to the heater 53 when the means 4A detects the presence of the dew formation.