Disclosed is an electrical capacitance sensor comprising: a board 10 having a one main surface and an other main surface; a sensor electrode 26 formed on the one main surface of the board 10 and detecting an electrical capacitance between the sensor electrode 26 and an object; a first guard electrode 25 formed on the one main surface of the board 10 and in a vicinity of the sensor electrode 26; and a second guard electrode 27 formed on the other main surface of the board 10, wherein a first terminal connecting portion 21 for the first guard electrode 25 and a second terminal connecting portion 23 for the second guard electrode 27 are provided at positions opposing each other.