A tire condition detecting device according to the present invention includes: an electronic component including a sensor configured to detect a tire condition; and a casing configured to house the electronic component. The casing includes a casing main body configured to house the electronic component and having an opening surface formed thereon, and a lid unit configured to cover the opening surface. An inside of the casing main body having the opening surface covered by the lid unit is filled with a sealant. Accordingly, tire conditions such as inner pressure and temperature of a tire can be surely detected and a breakdown of an electronic component can be prevented even in an environment where water content such as a coolant is injected in the tire.