A portable transmitter includes a circuit board having a button battery and an antenna; and a case accommodating the battery and the circuit board. The case includes first and second case members being engaged with each other. A concave portion is formed on the first or second case members to accommodate the button battery, and a lock portion is formed on the first or second case members to lock the circuit board. While the concave portion accommodates the button battery and the circuit board is locked by the lock portion, a surface of the circuit board and a surface of the button battery are attached, and the first case member and the second case member are engaged.