A muffler for an air-conditioning apparatus, comprising: a muffler main body, having a tubular shape, in which an inlet small diameter portion is connected to a large diameter portion through an enlarged diameter portion, and the large diameter portion is connected to an outlet small diameter portion through a reduced diameter portion; an inlet pipe connected to the inlet small diameter portion of the muffler main body; and an outlet pipe connected to the outlet small diameter portion of the muffler main body, the inlet pipe having an inserted pipe portion disposed in the muffler main body, the inserted pipe portion being inserted into the muffler main body from the inlet small diameter portion and extending from a starting point of the enlarged diameter portion to an inside of the muffler main body, the inserted pipe portion having an upper inserted pipe portion positioned on an inlet side of the muffler main body and a lower inserted pipe portion positioned on an outlet side of the muffler main body, wherein the upper inserted pipe portion has an inner diameter equal to an inner diameter of the inlet pipe on an upstream part of the inlet small diameter portion, and wherein the lower inserted pipe portion has a distal end positioned at a center of a length from an inlet to an outlet of the muffler main body, characterized in that the lower inserted pipe portion has an inner diameter smaller than an inner diameter of the upper inserted pipe portion, wherein a ratio of an inner diameter D of the muffler main body to an inner diameter D 2 of the lower inserted pipe portion is set to satisfy D/D 2 >5.7, and wherein, when a length of the upper inserted pipe portion is defined as L 2, and a length of the lower inserted pipe portion is defined as L 3, a ratio of L 3 to L 2 is set to satisfy 1.5<L 3 /L 2 <3. a muffler main body, having a tubular shape, in which an inlet small diameter portion is connected to a large diameter portion through an enlarged diameter portion, and the large diameter portion is connected to an outlet small diameter portion through a reduced diameter portion; an inlet pipe connected to the inlet small diameter portion of the muffler main body; and an outlet pipe connected to the outlet small diameter portion of the muffler main body, the inlet pipe having an inserted pipe portion disposed in the muffler main body, the inserted pipe portion being inserted into the muffler main body from the inlet small diameter portion and extending from a starting point of the enlarged diameter portion to an inside of the muffler main body, the inserted pipe portion having an upper inserted pipe portion positioned on an inlet side of the muffler main body and a lower inserted pipe portion positioned on an outlet side of the muffler main body, wherein the upper inserted pipe portion has an inner diameter equal to an inner diameter of the inlet pipe on an upstream part of the inlet small diameter portion, and wherein the lower inserted pipe portion has a distal end positioned at a center of a length from an inlet to an outlet of the muffler main body, characterized in that the lower inserted pipe portion has an inner diameter smaller than an inner diameter of the upper inserted pipe portion, wherein a ratio of an inner diameter D of the muffler main body to an inner diameter D 2 of the lower inserted pipe portion is set to satisfy D/D 2 >5.7, and wherein, when a length of the upper inserted pipe portion is defined as L 2, and a length of the lower inserted pipe portion is defined as L 3, a ratio of L 3 to L 2 is set to satisfy 1.5<L 3 /L 2 <3.