An intake passage structure for a turbocharger-equipped engine, the intake passage structure comprising: a compressor of the turbocharger housed in a compressor case; an upstream intake passage supplying intake air into the compressor case; a downstream intake passage supplying the intake air supplied into the compressor case and supercharged by the compressor to an intake port of the engine; and a throttle valve, wherein a supercharging passage and an air relief passage are provided in the compressor case, the supercharging passage including the compressor and connecting the upstream intake passage and the downstream intake passage together, the air relief passage connecting an upstream portion of the supercharging passage upstream of the compressor and a downstream portion of the supercharging passage downstream of the compressor together without passing through the compressor, and returning a portion of the intake air supercharged by the compressor to the upstream portion of the supercharging passage upstream of the compressor, the air relief passage has a first passage and a second passage, each of which is in a non-linear shape, the first and second passages (73, 74) each have an air outflow port (73a, 74a) formed through an inner wall surface of the upstream portion of the supercharging passage upstream of the compressor, the air outflow port of the first passage and the air outflow port of the second passage are formed through different portions of the inner wall surface in a circumferential direction of the inner wall surface so as to overlap with each other in a direction along a central axis of the upstream portion, and an upstream end of the air relief passage is connected to the downstream portion of the supercharging passage through a connection passage provided in the compressor case, characterized in that the throttle valve is disposed in the downstream intake passage, the first and second passages (73, 74) respectively have air inflow ports (73b, 74b) formed through the inner wall surface of the connection passage, and are arranged side by side in the vertical direction, and when the first and second passage (73, 74) are viewed from a direction along the central axis of the upstream portion, the first passage which is an upper one of these passages, is curved to protrude upward, and the second passage which is a lower one of these passages, is curved to protrude downward so that the first and second passages are curved to protrude away from each other. a compressor of the turbocharger housed in a compressor case; an upstream intake passage supplying intake air into the compressor case; a downstream intake passage supplying the intake air supplied into the compressor case and supercharged by the compressor to an intake port of the engine; and a throttle valve, wherein a supercharging passage and an air relief passage are provided in the compressor case, the supercharging passage including the compressor and connecting the upstream intake passage and the downstream intake passage together, the air relief passage connecting an upstream portion of the supercharging passage upstream of the compressor and a downstream portion of the supercharging passage downstream of the compressor together without passing through the compressor, and returning a portion of the intake air supercharged by the compressor to the upstream portion of the supercharging passage upstream of the compressor, the air relief passage has a first passage and a second passage, each of which is in a non-linear shape, the first and second passages (73, 74) each have an air outflow port (73a, 74a) formed through an inner wall surface of the upstream portion of the supercharging passage upstream of the compressor, the air outflow port of the first passage and the air outflow port of the second passage are formed through different portions of the inner wall surface in a circumferential direction of the inner wall surface so as to overlap with each other in a direction along a central axis of the upstream portion, and an upstream end of the air relief passage is connected to the downstream portion of the supercharging passage through a connection passage provided in the compressor case, characterized in that the throttle valve is disposed in the downstream intake passage, the first and second passages (73, 74) respectively have air inflow ports (73b, 74b) formed through the inner wall surface of the connection passage, and are arranged side by side in the vertical direction, and when the first and second passage (73, 74) are viewed from a direction along the central axis of the upstream portion, the first passage which is an upper one of these passages, is curved to protrude upward, and the second passage which is a lower one of these passages, is curved to protrude downward so that the first and second passages are curved to protrude away from each other.