To provide a heat transfer tube with inside grooves allowing fins sharper than conventional ones to be formed without increasing a fin rolling pressure extremely, thereby obtaining high condensing performance.

This heat transfer tube with inside grooves 1 has many fins 2 projecting from the surface of the inner periphery formed on the surface of the inner periphery of a metallic conduit, and the lower part 2C of the sidewall surface of the fin 2 has a steep slope. On the other hand, the upper part 2B of the sidewall surface of the fin 2 has a gentle slope with a tilt angle that is more obtuse than that of the lower part 2C of the sidewall surface of the fin having the steep slope.