An ultrasonic sensor that is less affected by humidity change is obtained. Ultrasonic sensor (1) is configured by sequentially laminating piezoelectric element (2), metal housing (3), first acoustic matching layer (4), and second acoustic matching layer (5). First acoustic matching layer (4) adjacent to piezoelectric element (2) with metal housing (3) interposed therebetween includes a thermoplastic resin and an inorganic filler. The weight fraction of the inorganic filler in first acoustic matching layer (4) is set to less than or equal to 30% and the weight fraction of the hollow structure filler in the inorganic filler is set to less than or equal to 50%.