To provide a vascular sap flow speed sensor having a size allowing measurement of the flow speed of vascular sap in a part of a plant such as a stem and capable of being manufactured at low cost. A vascular sap flow speed sensor 1 includes a heater sensor HS and a reference sensor RS. The heater sensor HS includes: a first probe unit 10a including a heat transfer plate 11 and a probe 12; a heater 20; a first temperature sensor 30a; and a first housing 40a in which the heat transfer plate 11, the heater 20, and the first temperature sensor 30a are housed. The reference sensor RS includes: a second probe unit 10b including a heat transfer plate 11 and a probe 12; a second temperature sensor 30b; and a second housing 40b in which the heat transfer plate 11 and the second temperature sensor 30b are housed. Each of the first probe unit 10a and the second probe unit 10b is made of a metallic material.