PURPOSE: To obtain a chemiluminescent element in which the closed part of a tube has a high resistance against leakage when the pressure in the tube increases.

CONSTITUTION: A tube 1 includes at least one diaphragm or a disc 4 separating the tube 1 into rooms 2 and 3 between end parts 5 thereof. The diaphragm or disc 4 has an almost rectangular section, and they are of almost circular shape and arranged at a right angle against the axis of the tube 1. Its edge is continuously in contact with the inside of tube wall. The elasticity and outer diameter and inner diameter of the tube 1 and the diameter and thickness of the diaphgram or disc 4 are selected in a manner that the diaphragm or disc 4 can be tilted by applying a torque to the outer wall of the tube 1 by means of simple pressurizing and manual means or by an equivalent method. Both ends 5 of the tube 1 are closed by melting its side wall, and the melted section is substantially within a flat plane.