To provide a neutron-detecting apparatus that can prevent detection sensitivity from being changed even if a neutron is received.

A detection section 12 is equipped with an external electrode 22 having a neutron-sensitive substance 23 and an internal electrode 31. An argon gas 34 is enclosed between the external and internal electrodes 22 and 31. The argon gas of an insulator 74 of an MI coaxial cable 13 at a base edge side and the argon gas 34 are airtightly separated by a base-edge-side sealing section 51 having an insulator 59 made of silicon nitride. The silicon nitride is used for the insulator 59, thus preventing the argon gas 34 from flowing to the insulator 59 or the periphery due to cracks or the like as compared with aluminum since change in volume is small and expansion cannot be easily made even if the neutron is applied to the silicon nitride, and hence preventing change in sensitivity due to change in the pressure of the argon gas 34. Since the insulator 59 has a fusiform shape, stress orthogonally crossing in an axial direction can be dispersed in the axial direction, thus preventing deterioration in performance.