Motor with deceleration mechanism

A motor with a deceleration mechanism, including:

• a motor part having a rotation shaft;
• and a deceleration mechanism part having the deceleration mechanism for decelerating rotation of the rotation shaft, the motor with the deceleration mechanism comprising:
• a housing which accommodates the deceleration mechanism;
• a communication hole which is provided in the housing and allows communication between an inside and an outside of the housing;
• a cylindrical member which is provided outside the housing, which extends in an axial direction of the communication hole, and of which an inside communicates with the communication hole;
• and
• at least one slit which is provided in the cylindrical member and extend in an axial direction of the cylindrical member,
• wherein an opening width of the at least one slit in a circumferential direction of the cylindrical member is narrower on an outer side than on an inner side of the cylindrical member,
• wherein each tip end side of the at least one slit on the outer side of the cylindrical member is tapered in the circumferential direction of the cylindrical member.